For several weeks I have been trying to wake up 3 hours after I go to sleep to wbtb, and not only have I been unable to wake up that early, but I also have only had a few lucids out of all the times I did wake up. However, I have tried 6 hours, and not only do I always wake up, but every time I have done it I have had a lucid (4 for 4) even if I stay in bed and fall back asleep without getting up for a period of time.