/highset if($nick(#channel,0) > %highestPeeps) {/set %highestPeeps $nick(#channel,0) | /set %highestPeepTime $fulldate}
I think spacing is your issue:
/highset if ($nick(#channel,0) > %hightestPeeps) { set %highestPeeps $nick(#channel,0) | set %highestPeepsTime $fulldate }
You need to have spaces after {'s and |'s and before }'s.
