after waking up from sleep right before or during REM cycle i don't think it matters how long your awake for, as long as your not too tired that youll just fall back asleep and also as long as your not too awake that you can't fall back asleep (while still conscious ofcourse) at all. Ive read around 30-60 minutes people would stay awake for. but its really what works for you. Im kind of in the same boat as you, im having trouble succeeding in a WILD. Furthest ive got was HI but that eventually goes away and nothing happens so i just go to sleep. maybe i just have to wait longer