30-90 minutes?! That's WBTB (wake back to bed). What he's saying about time is that you will lose 30-60 minutes of sleep when attempting WILD. That's because the relaxation phase takes very long time. You only need to wake up that much so that you don't fall asleep normally but can relax and stay conscious. You could try ~5 minutes at first and then change it if you're too tired or too awake.