Taking low-dose melatonin upon waking can delay the natural drop in melatonin, causing the day to start later and potentially leading to staying up later.

“Same thing as if you take that lowd dose melatonin as soon as you wake up in the morning. that drop gets delayed a little bit. So it ends so that ball lands a little further along than it expected to. So your day started a little bit later than it thought it was going to. So you'll stay up a little bit later the next time.”