For your first problem, I think you've simply hit mIRC's pernickity state regarding spaces. Putting a space before the last brace should do the trick.
Regarding your second query, the following should do the trick
.timeranti.idle 0 600 .msg $me Still here
Every time you make an entry the timer will reset, so the only time it will hit 600 seconds (10 minutes) is if you don't type anything for those 10 minutes. At that time (if it occurs) you'll send yourself a pm (private message) saying Still here. This will keep you from interrupting a channel with the message (noting as how it is an automated message)