How long can you wait to claim a gift?

I've been looking for this answer before, but I still don't know it.
Let's say I enter a giveaway right before I go to bed, (and the giveaway lasts 1hour)
and let's pretend I win... but i'm asleep so I don't know untill I wake up.

Will there be drawn another winner because I don't respond or can I claim the gift when i wake up.
I know it'll probably be the 2nd, but I just want to be sure...
How long can one wait before claiming the gift?

thx guys