I really think that a triggerable timer would really have its uses in SP games. Here are some scenarios I think might benefit from it:
- The player has just killed the boss creature of the map. He now has 5 minutes to evacuate to a safe area or he will be trapped in the place he has entered.
- The player has just been briefed on his mission, and he has bypassed the alarms. He now has 15 minutes to accomplish his mission before the alarms sound, which would suddenly make his mission a lot more difficult. (CreatureFactories suddenly double the number of enemies in the level, or something.)
- The player has activated the auto-destruct sequence on the Skaarj vessel he infiltrated. The player has 10 minutes to fight his way to an escape pod and pilot it to a safe distance.