Why do this only when you run a command? mIRC has events like on JOIN, on PART, on NICK and timers. Just have a script check if someone is in the correct channel when he enters the other channel. If you want a short time to comply, put the test in a 30 second timer or something before checking. Also check on part so that so one just parts the required channel after a few minutes. Probably best to give the timers a name that is related to the nickname, so you can disable the timer when nick joins channel2 and can change the timer when he changes his nick during those 30 seconds...
No need to remember to run the alias every few hours or so, just have it done automatically. This also prevents having to kick 20 people at once (flood) if it's a big channel...
