Don't stay up too long. Basically, if you have ever woken up before, gone to the loo, and fall asleep immeadatly afterwards, you will need to stay up longer. Woken up, gone to the loo, then tossed and turned? Probably need to stay in bed. Woken up gone to the loo, and fall asleep after a few minutes, perfect. Also, be prepared to be tossing and turning for the first few WBTBs. That's what happened to me.

People say that stay up shorter to MILD and longer to WILD.