For example, to wake up at 7:00 a.m., you could go to bed at 10:00 p.m. for six 90-minute cycles (9 hours of sleep) or 11:30 p.m. for five cycles (7.5 hours of sleep). Deep sleep is when your body repairs and restores itself, and dream-filled REM sleep allows your brain to process emotions and consolidate memories. Credit: Mayo ClinicA single sleep cycle typically lasts around 90 minutes, says Dr. Andrea Matsumura, a board-certified sleep medicine physician and founder of the Sleep Goddess Method. Jade Wu, a board-certified sleep psychologist, agrees that the 90-minute sleep cycle hack is not scientifically sound. “There’s no way to predict or regulate cycles to be exactly 90 minutes.”As the night progresses, sleep cycles tend to get longer, with the first sleep cycle ranging from 70 to 100 minutes, and later cycles lasting between 90 and 120 minutes.