I think the problem here is you just want mIRC to do everything for you, and if thats the case then scripting isn't needed. If this is added then all of these should be added as well

/timer -d [day]
trigger a timer on a specific day of the week.
/timer -c [#channel]
trigger the timer only if I'm on #channel
/timer -u [uptime]
trigger the timer after mIRC has been running for uptime seconds
/timer -U [uptime]
trigger the timer after Windows has been running for uptime seconds

All of those suggestions are just as equally valid. If your suggestion is deemed to be needed, then so are each of the ones I just mentioned; sure they can be scripted, but thats "too complex"