As i understand it mirc doesnt really have timers as such, rather it has a timer list, that it checks once per second, and see if if any have elapsed and need triggring.
now assuming im correct (which im not saying in anyway i am) about how mirc pre pharses the scripts for events, it wouldnt be hard for it also check a setting to see if any on Away events existed, I however have also looked at the way you suggested, and the more i look at it now the more i see how it could well be as usefull if not more, maybe just a little harder (newer/different lol) to code to.
PS: above meaning per second timers of course, i alsoe beleive the -m timers work the same way but on a faster cycle rate 64 or 100 times per second checked, dependent on OS, likely the os's program cycle rate or some such thing.
