You could put this into aliases:
/active_on /timerActive 0 1800 msg #<channel> Hi
/active_off /timerActive off
This will repeat 'Hi' every 30 minutes when you type in /active_on into the mirc window. And it will stop when you type /active_off. The '1800' is the ammount off seconds inbetween each message.
You could also type this into aliases:
/leave_on /timerLeave 0 3600 msg #<channel> /part
/leave_off /timerLeave off
This works the same way, when you type in /leave_on you will leave the channel every hour.
Hope this helps and if you have anything else you need, I or anyone else on the forums would be happy to help.