it has been explained in other threads on this forum, but timers and so on are just not accurate
a simple test would be these two aliases using $ticks and the millisecond timer
run it a few times and watch the decimal difference drift
it is what it is
timertest {
set -u30 %starticks $ticks
timertest -m 5 1000 timertest2 $!ticks
}
timertest2 {
echo -a . $calc(($ticks - %starticks) / 1000))
}