diff --git a/Makefile b/Makefile
--- a/Makefile
+++ b/Makefile
@@ -396,7 +396,7 @@
 	@echo
 	@false
 
-STARTTIME!= LC_ALL=C date
+STARTTIME!= date -Iseconds
 CHECK_TIME!= cmp=`mktemp`; find ${.CURDIR}/sys/sys/param.h -newer "$$cmp" && rm "$$cmp"; echo
 .if !empty(CHECK_TIME)
 .error check your date/time: ${STARTTIME}
@@ -433,7 +433,7 @@
 .endif
 	@echo
 	@echo "--------------------------------------------------------------"
-	@echo ">>> make world completed on `LC_ALL=C date`"
+	@echo ">>> make world completed on `date -Iseconds`"
 	@echo "                   (started ${STARTTIME})"
 	@echo "--------------------------------------------------------------"
 .else
@@ -611,7 +611,7 @@
 
 universe-toolchain: .PHONY universe_prologue
 	@echo "--------------------------------------------------------------"
-	@echo "> Toolchain bootstrap started on `LC_ALL=C date`"
+	@echo "> Toolchain bootstrap started on `date -Iseconds`"
 	@echo "--------------------------------------------------------------"
 	${_+_}@cd ${.CURDIR}; \
 	    env PATH=${PATH:Q} ${SUB_MAKE} ${JFLAG} kernel-toolchain \
@@ -636,7 +636,7 @@
 	    false; \
 	fi
 	@echo "--------------------------------------------------------------"
-	@echo "> Toolchain bootstrap completed on `LC_ALL=C date`"
+	@echo "> Toolchain bootstrap completed on `date -Iseconds`"
 	@echo "--------------------------------------------------------------"
 
 .for target in ${_UNIVERSE_TARGETS}
@@ -644,7 +644,7 @@
 universe_epilogue: universe_${target}
 universe_${target}: universe_${target}_prologue .PHONY
 universe_${target}_prologue: universe_prologue .PHONY
-	@echo ">> ${target} started on `LC_ALL=C date`"
+	@echo ">> ${target} started on `date -Iseconds`"
 universe_${target}_worlds: .PHONY
 
 .if !make(targets) && !make(universe-toolchain)
@@ -703,7 +703,7 @@
 universe_${target}_prologue: universe-toolchain
 .endif
 universe_${target}_${target_arch}: universe_${target}_prologue .MAKE .PHONY
-	@echo ">> ${target}.${target_arch} ${UNIVERSE_TARGET} started on `LC_ALL=C date`"
+	@echo ">> ${target}.${target_arch} ${UNIVERSE_TARGET} started on `date -Iseconds`"
 	@(cd ${.CURDIR} && env __MAKE_CONF=/dev/null \
 	    ${SUB_MAKE} ${JFLAG} ${UNIVERSE_TARGET} \
 	    TARGET=${target} \
@@ -713,7 +713,7 @@
 	    (echo "${target}.${target_arch} ${UNIVERSE_TARGET} failed," \
 	    "check _.${target}.${target_arch}.${UNIVERSE_TARGET} for details" | \
 	    ${MAKEFAIL}))
-	@echo ">> ${target}.${target_arch} ${UNIVERSE_TARGET} completed on `LC_ALL=C date`"
+	@echo ">> ${target}.${target_arch} ${UNIVERSE_TARGET} completed on `date -Iseconds`"
 .endfor
 .endif # ${__DO_WORLDS} == "yes"
 
@@ -728,16 +728,16 @@
 # Tell the user the worlds and kernels have completed
 universe_${target}: universe_${target}_done
 universe_${target}_done:
-	@echo ">> ${target} completed on `LC_ALL=C date`"
+	@echo ">> ${target} completed on `date -Iseconds`"
 .endfor
 .if make(universe_kernconfs) || make(universe_kernels)
 .if !defined(TARGET)
 TARGET!=	uname -m
 .endif
 universe_kernels_prologue: .PHONY
-	@echo ">> ${TARGET} kernels started on `LC_ALL=C date`"
+	@echo ">> ${TARGET} kernels started on `date -Iseconds`"
 universe_kernels: universe_kernconfs .PHONY
-	@echo ">> ${TARGET} kernels completed on `LC_ALL=C date`"
+	@echo ">> ${TARGET} kernels completed on `date -Iseconds`"
 .if defined(MAKE_ALL_KERNELS)
 _THINNER=cat
 .elif defined(MAKE_LINT_KERNELS)
@@ -761,7 +761,7 @@
 .endif
 universe_kernconfs_${TARGET_ARCH_${kernel}}: universe_kernconf_${TARGET}_${kernel}
 universe_kernconf_${TARGET}_${kernel}: .MAKE
-	@echo ">> ${TARGET}.${TARGET_ARCH_${kernel}} ${kernel} kernel started on `LC_ALL=C date`"
+	@echo ">> ${TARGET}.${TARGET_ARCH_${kernel}} ${kernel} kernel started on `date -Iseconds`"
 	@(cd ${.CURDIR} && env __MAKE_CONF=/dev/null \
 	    ${SUB_MAKE} ${JFLAG} buildkernel \
 	    TARGET=${TARGET} \
@@ -771,7 +771,7 @@
 	    > _.${TARGET}.${kernel} 2>&1 || \
 	    (echo "${TARGET} ${kernel} kernel failed," \
 	    "check _.${TARGET}.${kernel} for details"| ${MAKEFAIL}))
-	@echo ">> ${TARGET}.${TARGET_ARCH_${kernel}} ${kernel} kernel completed on `LC_ALL=C date`"
+	@echo ">> ${TARGET}.${TARGET_ARCH_${kernel}} ${kernel} kernel completed on `date -Iseconds`"
 .endfor
 .for target_arch in ${TARGET_ARCHES_${TARGET}}
 universe_kernconfs: universe_kernconfs_${target_arch} .PHONY
@@ -781,7 +781,7 @@
 universe: universe_epilogue
 universe_epilogue: .PHONY
 	@echo "--------------------------------------------------------------"
-	@echo ">>> make universe completed on `LC_ALL=C date`"
+	@echo ">>> make universe completed on `date -Iseconds`"
 	@echo "                      (started ${STARTTIME})"
 	@echo "--------------------------------------------------------------"
 .if defined(DOING_TINDERBOX)
diff --git a/Makefile.inc1 b/Makefile.inc1
--- a/Makefile.inc1
+++ b/Makefile.inc1
@@ -385,7 +385,7 @@
 				LINKER_FREEBSD_VERSION
 toolchain-metadata.mk: .PHONY .META
 	@: > ${.TARGET}
-	@echo ".info Using cached toolchain metadata from build at $$(hostname) on $$(date)" \
+	@echo ".info Using cached toolchain metadata from build at $$(hostname) on $$(date -Iseconds)" \
 	    > ${.TARGET}
 	@echo "_LOADED_TOOLCHAIN_METADATA=t" >> ${.TARGET}
 .for v in ${_TOOLCHAIN_METADATA_VARS}
@@ -1283,13 +1283,13 @@
 
 buildworld_prologue: .PHONY
 	@echo "--------------------------------------------------------------"
-	@echo ">>> World build started on `LC_ALL=C date`"
+	@echo ">>> World build started on `date -Iseconds`"
 	@echo "--------------------------------------------------------------"
 
 buildworld_epilogue: .PHONY
 	@echo
 	@echo "--------------------------------------------------------------"
-	@echo ">>> World build completed on `LC_ALL=C date`"
+	@echo ">>> World build completed on `date -Iseconds`"
 	@seconds=$$(($$(date '+%s') - ${_BUILDWORLD_START})); \
 	  echo ">>> World built in $$seconds seconds, ncpu: $$(${_ncpu_cmd})${.MAKE.JOBS:S/^/, make -j/}"
 	@echo "--------------------------------------------------------------"
@@ -1342,11 +1342,11 @@
 installcheck: _installcheck_world _installcheck_kernel .PHONY
 _installcheck_world: .PHONY
 	@echo "--------------------------------------------------------------"
-	@echo ">>> Install check world started on `LC_ALL=C date`"
+	@echo ">>> Install check world started on `date -Iseconds`"
 	@echo "--------------------------------------------------------------"
 _installcheck_kernel: .PHONY
 	@echo "--------------------------------------------------------------"
-	@echo ">>> Install check kernel started on `LC_ALL=C date`"
+	@echo ">>> Install check kernel started on `date -Iseconds`"
 	@echo "--------------------------------------------------------------"
 
 #
@@ -1635,14 +1635,14 @@
 .endif
 	@echo
 	@echo "--------------------------------------------------------------"
-	@echo ">>> Installing everything started on `LC_ALL=C date`"
+	@echo ">>> Installing everything started on `date -Iseconds`"
 	@echo "--------------------------------------------------------------"
 	${_+_}cd ${.CURDIR}; ${MAKE} -f Makefile.inc1 install
 .for libcompat in ${libcompats}
 	${_+_}cd ${.CURDIR}; ${MAKE} -f Makefile.inc1 install${libcompat}
 .endfor
 	@echo "--------------------------------------------------------------"
-	@echo ">>> Installing everything completed on `LC_ALL=C date`"
+	@echo ">>> Installing everything completed on `date -Iseconds`"
 	@seconds=$$(($$(date '+%s') - ${_INSTALLWORLD_START})); \
 	  echo ">>> Install world completed in $$seconds seconds, ncpu: $$(${_ncpu_cmd})${.MAKE.JOBS:S/^/, make -j/}"
 	@echo "--------------------------------------------------------------"
@@ -1795,7 +1795,7 @@
 	@echo
 .for _kernel in ${BUILDKERNELS:Ndummy}
 	@echo "--------------------------------------------------------------"
-	@echo ">>> Kernel build for ${_kernel} started on `LC_ALL=C date`"
+	@echo ">>> Kernel build for ${_kernel} started on `date -Iseconds`"
 	@echo "--------------------------------------------------------------"
 	@echo "===> ${_kernel}"
 	mkdir -p ${KRNLOBJDIR}
@@ -1837,7 +1837,7 @@
 	@echo "--------------------------------------------------------------"
 	${_+_}cd ${KRNLOBJDIR}/${_kernel}; ${KMAKE} all -DNO_MODULES_OBJ
 	@echo "--------------------------------------------------------------"
-	@echo ">>> Kernel build for ${_kernel} completed on `LC_ALL=C date`"
+	@echo ">>> Kernel build for ${_kernel} completed on `date -Iseconds`"
 	@echo "--------------------------------------------------------------"
 
 .endfor
@@ -1868,14 +1868,14 @@
 	false
 .endif
 	@echo "--------------------------------------------------------------"
-	@echo ">>> Installing kernel ${INSTALLKERNEL} on $$(LC_ALL=C date)"
+	@echo ">>> Installing kernel ${INSTALLKERNEL} on $$(date -Iseconds)"
 	@echo "--------------------------------------------------------------"
 	${_+_}cd ${KRNLOBJDIR}/${INSTALLKERNEL}; \
 	    ${CROSSENV} PATH=${TMPPATH:Q} \
 	    ${MAKE} ${IMAKE_INSTALL} KERNEL=${INSTKERNNAME} METALOG=${METALOG} \
 	    ${.TARGET:S/kernel//}
 	@echo "--------------------------------------------------------------"
-	@echo ">>> Installing kernel ${INSTALLKERNEL} completed on $$(LC_ALL=C date)"
+	@echo ">>> Installing kernel ${INSTALLKERNEL} completed on $$(date -Iseconds)"
 	@echo "--------------------------------------------------------------"
 	@seconds=$$(($$(date '+%s') - ${_INSTALLKERNEL_START})); \
 	  echo ">>> Install kernel(s) ${INSTALLKERNEL} completed in $$seconds seconds, ncpu: $$(${_ncpu_cmd})${.MAKE.JOBS:S/^/, make -j/}"
@@ -1884,14 +1884,14 @@
 .if ${BUILDKERNELS:[#]} > 1 && ${NO_INSTALLEXTRAKERNELS} != "yes"
 .for _kernel in ${BUILDKERNELS:[2..-1]}
 	@echo "--------------------------------------------------------------"
-	@echo ">>> Installing kernel ${_kernel} $$(LC_ALL=C date)"
+	@echo ">>> Installing kernel ${_kernel} $$(date -Iseconds)"
 	@echo "--------------------------------------------------------------"
 	${_+_}cd ${KRNLOBJDIR}/${_kernel}; \
 	    ${CROSSENV} PATH=${TMPPATH:Q} \
 	    ${MAKE} ${IMAKE_INSTALL} KERNEL=${INSTKERNNAME}.${_kernel} METALOG=${METALOG} \
 	    ${.TARGET:S/kernel//}
 	@echo "--------------------------------------------------------------"
-	@echo ">>> Installing kernel ${_kernel} completed on $$(LC_ALL=C date)"
+	@echo ">>> Installing kernel ${_kernel} completed on $$(date -Iseconds)"
 	@echo "--------------------------------------------------------------"
 .endfor
 	@seconds=$$(($$(date '+%s') - ${_INSTALLKERNEL_START})); \
diff --git a/stand/common/newvers.sh b/stand/common/newvers.sh
--- a/stand/common/newvers.sh
+++ b/stand/common/newvers.sh
@@ -45,12 +45,12 @@
 LC_ALL=C; export LC_ALL
 u=${USER-root} h=${HOSTNAME-`hostname`}
 if [ -n "$SOURCE_DATE_EPOCH" ]; then
-	if ! t=$(date -ur $SOURCE_DATE_EPOCH 2>/dev/null); then
+	if ! t=$(date -ur $SOURCE_DATE_EPOCH -Iseconds 2>/dev/null); then
 		echo "Invalid SOURCE_DATE_EPOCH" >&2
 		exit 1
 	fi
 else
-	t="${NEWVERS_DATE:-`date`}"
+	t="${NEWVERS_DATE:-`date -Iseconds`}"
 fi
 r=`awk -F: ' /^[0-9]\.[0-9]+:/ { print $1; exit }' $1`
 
diff --git a/sys/conf/newvers.sh b/sys/conf/newvers.sh
--- a/sys/conf/newvers.sh
+++ b/sys/conf/newvers.sh
@@ -194,12 +194,12 @@
 d=$builddir
 h=${HOSTNAME:-$(hostname)}
 if [ -n "$SOURCE_DATE_EPOCH" ]; then
-	if ! t=$(date -ur $SOURCE_DATE_EPOCH 2>/dev/null); then
+	if ! t=$(date -ur $SOURCE_DATE_EPOCH -Iseconds 2>/dev/null); then
 		echo "Invalid SOURCE_DATE_EPOCH" >&2
 		exit 1
 	fi
 else
-	t=$(date)
+	t=$(date -Iseconds)
 fi
 i=$(${MAKE:-make} -V KERN_IDENT)
 compiler_v=$($(${MAKE:-make} -V CC) -v 2>&1 | grep -w 'version')
diff --git a/usr.sbin/bsdinstall/scripts/auto b/usr.sbin/bsdinstall/scripts/auto
--- a/usr.sbin/bsdinstall/scripts/auto
+++ b/usr.sbin/bsdinstall/scripts/auto
@@ -171,7 +171,7 @@
 
 ############################################################ MAIN
 
-f_dprintf "Began Installation at %s" "$( date )"
+f_dprintf "Began Installation at %s" "$(date -Iseconds)"
 
 environment_save
 
@@ -482,7 +482,7 @@
 bsdinstall entropy
 bsdinstall umount
 
-f_dprintf "Installation Completed at %s" "$( date )"
+f_dprintf "Installation Completed at %s" "$(date -Iseconds)"
 
 ################################################################################
 # END
diff --git a/usr.sbin/bsdinstall/scripts/jail b/usr.sbin/bsdinstall/scripts/jail
--- a/usr.sbin/bsdinstall/scripts/jail
+++ b/usr.sbin/bsdinstall/scripts/jail
@@ -149,7 +149,7 @@
 
 : ${BSDDIALOG_OK=0}
 
-f_dprintf "Began Installation at %s" "$( date )"
+f_dprintf "Began Installation at %s" "$(date -Iseconds)"
 
 if [ -z "$1" ]; then
 	error "Directory can not be empty\n\nUsage:\nbsdinstall jail directory"
@@ -223,7 +223,7 @@
 
 bsdinstall entropy
 
-f_dprintf "Installation Completed at %s" "$(date)"
+f_dprintf "Installation Completed at %s" "$(date -Iseconds)"
 exit $SUCCESS
 
 ################################################################################
diff --git a/usr.sbin/bsdinstall/scripts/script b/usr.sbin/bsdinstall/scripts/script
--- a/usr.sbin/bsdinstall/scripts/script
+++ b/usr.sbin/bsdinstall/scripts/script
@@ -85,7 +85,7 @@
 SCRIPT="$1"
 shift
 
-f_dprintf "Began Installation at %s" "$( date )"
+f_dprintf "Began Installation at %s" "$(date -Iseconds)"
 rm -rf $BSDINSTALL_TMPETC
 mkdir $BSDINSTALL_TMPETC
 rm -f $TMPDIR/bsdinstall-installscript-setup
@@ -105,7 +105,7 @@
 	export debugFile="$BSDINSTALL_LOG"
 	f_quietly f_debug_init
 	# NB: Being scripted, let debug go to terminal for invalid debugFile
-	f_dprintf "Began Installation at %s" "$( date )"
+	f_dprintf "Began Installation at %s" "$(date -Iseconds)"
 fi
 
 # Make partitions
@@ -177,7 +177,7 @@
 	zpool export $ZFSBOOT_POOL_NAME
 fi
 
-f_dprintf "Installation Completed at %s" "$( date )"
+f_dprintf "Installation Completed at %s" "$(date -Iseconds)"
 
 trap - EXIT
 exit $SUCCESS