Edit: Added the function to jail someone in minutes instead, since that was a bit mroe usfull for me.
So, incase you want to use minutes instead of seconds, change line (32) from (var %timer = $3) to (var %timer = $3 * 60) and line (34) from \'(\' ( $+ $duration($3) $+ ). \')\' to \'(\' ( $+ $duration(%timer,$3) $+ ). \')\'
You could just edit the snippet of yours...