First of all, you're missing ending )'s there... but that won't work anyhow.
You need to use -u to set a timed ban. /help /ban
Example:
/ban -u600 chan nick
This would ban for 600seconds (5 minutes). You use the same idea when using -k. Note that I'd just end the kick reason with "banned for 24 hours" rather than even messing with $duration... there's no reason to use $duration for this.
