The runtime value is multiplied by 1000000, but it is already in microseconds, resulting in a very large estimate.
Removing this extra factor of 1000000 should fix bug #235556.
Note that this estimate is only used for short-lived processes.
The patch works like a charm! This fixes the case I described here (https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=235556#c2), the stats are now correct: https://www.bsdstore.ru/trash/racct.png
Tested on: FreeBSD 14.0-CURRENT #0 main-n247127-1976e079544-dirty