Melatonin is not a sleep drug your body makes. It is a signal that tells the rest of you the sun has gone down.
That signal is triggered by darkness and switched off by light. Not by the clock, not by how tired you are — by what reaches your eyes. Light at the wrong hour delays the signal, and the whole night shifts later behind it.
This is why a mask that leaks at the bridge of the nose is not almost as good. It is the gap that does the work.
