Why are they doing it? Because someone asked them to, or because on their own they decided it was worth doing.'Your mission is to [do thing] by [time X] or else [bad thing Y] happens.'
I suppose you could have a quest of just 'do thing' but that sounds awfully boring. Like... why are they doing it? What happens if they fail? How long do they have to do the thing?
What happens if they fail? They fail, which may - but doesn't have to - have consequences down the road.
How long do they have? As long as it takes. Maybe they don't even go straight to the McGuffin mission but instead detour on the way to the old ruined tower they've been meaning to check out for ages, and put the McGuffin job aside for later.
Personally, I usually prefer type 1.Compare the following quests:
1) You need to recover/ destroy/ locate/ stop the Mcguffin. Whenever you get around to it. Time is not of the essence.
2) You need to recover/ destroy/ locate/ stop the Mcguffin before [time X] or else [bad thing Y] happens. Time is of the essence.
That way, I-as-player and I-as-PC have time to - with the party - gather whatever information we can before leaving, use this information to recruit NPC adventurers to fill any obvious gaps in our lineup, then once in site fully explore whatever it is we're doing and-or wherever it is we're at, take time to thoroughly search the place and make sure we didn't miss anything, and then come back to town, take our time over training and treasury division, and enjoy some downtime.
Were I fed a constant diet of type 2 adventures, sooner or later I'd end up saying "Screw it. This time the world can fall apart, either that or someone else can do this mission. I think we should go back to that last place - we were so rushed that I'm 99% sure we missed half of it."
It can be impactful once in a while, and thus is useful to do once in a while. But not all the time.Which is more impactful, gives the Players a feeling that they've accomplished something, and exercised their agency to affect the game world (stopping a bad thing from happening, via performing the quest).
Quite right - time limits are an overused means of generating tension in movies and TV too.Heroes in movies dont have all the time in the world to defuse the bomb, save their daughter from evil mercenaries, blow up the Death Star before it destroys Yavin IV, recover the Ark of the Covenant etc, so why should your heroes?