For everyone else...
Since I assume that the answer was passed along in a PM, I will help eveyone else understand the principle behind the "Night" talkgroup....
The "Night" talkgroups are used for dispatch only. They do not use voice pagers in Charleston, and the night talkgroup allows the dispatcher to send the dispatch and redirect the rest of the response traffic to a operations talkgroup. This way you don't keep all 5 stations (example) up all night while 1 engine is handling a MVA.
The stations move to the talkgroup a pre-determined time each NIGHT.