Zebrah's right, it's pretty difficult to WILD before sleeping around 5 hours! You'll probably end up spending an hour in SP, then enter a dream that's either unstable or short. So do a WBTB in the middle of the night if possible - stay up until you feel rather awake, but not so awake you won't be able to settle back into bed. You still might end up falling asleep at first, but that's part of finding how long you should stay up for. Some people take five minutes, others take half an hour or longer; it's different for everyone.

The point of WILD is to fall asleep while maintaining awareness - if you still find yourself falling asleep, try using a different anchor - count, listen to ambient noise, listen to your breathing, etc. Don't get too preoccupied though. You know you're getting close when your thoughts start to become wierd, nonsensical or unusual; at this point, bring your attention back to staying conscious. Keep still, and keep relaxing, then you'll eventually enter SP and a dream!