If building (custom) FreeBSD images people tend to patch param.h.  In case
this happens just before the build is started (within the same second)
CHECK_TIME actually triggers thinking param.h is in the future (see f_Xtime,
c_Xtime logi in find(1) sources for the details in !F_EXACTTIME case).
Using the -mtime -0s (seconds, rather than no unit) avoids this 1s race.