You'll need to make a user level for "mods". I would go more in depth but I have to leave REALLY soon. But here's the code... =/ I forgot how to make part of this a "Code:" -- my horrible memory.

on mods:TEXT:!dvoice:#:{
/mode # -v $$2
/msg # 4,1 $$2 's voice has been taken away for $$3 seconds.
/msg # 12,1 Reason: $4-
/timer 1 $$3 /mode # +v $$2
}
on mods:TEXT:!voice:#:/mode # +v $$2

With the "mods" level, it'll only allow whoever has that user level to use it, not just everyone in the room. I also have a way to keeping people muted when they exit and come back but I'm pressed for time. If no one else posts a way of doing this, I will tonight. Sadly this only works for seconds, again if no one posts a minutes version, I'll do so tonight. I quickly grabbed this off of my old bot needs some re-working. But this should get you going.