I used to use sleepyti.me until it was bought by some shitty company that sells mattresses or something and subsequently went to ugly bloated ad-infested "modernized" shit.

I just checked again for the first time in a while and it seems to have improved since it was first redesigned, though it's still not as simple and lightweight as it once was.

Anyways. It helped when I used it. Kept a shortcut right on my home screen for the longest time. If you can look past the stupid brand name they've chosen to redirect to, it's worth a shot.