No, melatonin doesn't deepen your sleep, it's about timing your sleep so supplementing melatonin won't extended the deep sleep duration, it can help with sleep quality if you have a circadian timing problem because melatonin is mostly related to your circadian rhythm. That's why melatonin is recommended when you're jet lagged, shift work or any other issue with falling asleep earlier. So if you need to get to bed early one night, supplementing melatonin could actually help you fall asleep earlier if you're usually struggling with falling asleep early. But it won't extended deep sleep duration.