I wouldnt use the -uN option anyway, not as it is right now.
The -uN options seems to act like the -z option, rather than waiting N seconds then unsetting, it decreases N by one once per second then unsets when N reaches zero.
Say u go "set -u10 %test BLAH" and then 4 seconds later the N value would be down to 6 and then another script executes that causes a large time delay say 15 seconds, when that script finishes, N still equals 6 and 6 seconds later %test is unset.
Thats alot different from going "set %test BLAH | .timer 1 10 unset %test", after the 4 seconds the other script goes off, and after that 15 seconds the timer goes off and %test unsets, even thats not an exact 10 seconds but we all know timers dont run tell the running script stops.