Having a hanging time limit before the village is overrun is just poor design. Shit doesn't work like that, gnolls aren't time bombs.
You're being stupid. Stop it. You're usually not stupid.
In case of approaching Doom quests the quest-givers could simply ask you to deal with it ASAP (eg. because the amassing gnolls not only threaten the village but also impede trade and kill unlucky travellers, etc.). The longer it takes you, the lower the reward you get, while the quest itself gets more difficult because the encroaching Doom amasses more forces and fortifies it's position.
Another example would be a burning house. You're asked to put out the fire. Either use ice/water spells or call fire fighters. Does it make sense to come back after doing 20 fedex quests, 2 main quest episodes and resting 8 times, so perhaps 3 in-game weeks and casting a hail storm? No, of course not. Yet you,
Excidium and
Jaesun call time limits arbitrary...
Edit: Weren't you guys some of the people who bitched about the Oblivion Gates never posing a threat and just sitting there until the player got around to dealing with them?