Change The Time Limit
From CustomCoD Wiki
You can change the time limit from the command line by setting the following dvars depending on the game mode you are playing. This sets each game mode to 30 minutes.
+set scr_dm_timelimit 30 (free for all)
+set scr_war_timelimit 30 (team deathmatch)
+set scr_sd_timelimit 30 (search and destroy)
+set scr_dom_timelimit 30 (domination)
Source Treyarch Wiki