I've been wondering that as well, but I haven't tested it. I would think you have to collect it within the time limit for it to count, since normal tasks don't count as complete until you collect them.
Another thing I've been wondering is, let's say Task 1 is 4 hours, and Task 2 is 4 hours, could you start Task 1, wait 2 hours, then start Task 2, so with the overlap the whole thing would only take 6 hours instead of 8? (Or any amount of time really, I'm just using this as an example). Obviously this would only work if the task is already available, but I considered doing it last night since the last task was just Lisa making a musical instrument, which is already a regular task, so I thought I could overlap it with Ned's task and it would be done faster. I wasn't brave enough to try it though.
