According to the Late Great Alexander Shulgin the recommended dose is 1-10mg orally.

TiHKAL #35 Melatonin with an exceptionally long Extensions and Commentary section: https://isomerdesign.com/PiHKAL/read.php?domain=tk&id=35

1mg in a pill that dissolves under the tongue works great for me. Very fast.

Doesn’t knock me out. But, if I’m already on the way to sleep, it gets me there faster. And, the sleep is a lot deeper. Wackier dreams right into the morning. More rested when I wake up.

If I know I’m going to have a hard time falling asleep, I’ll wait a bit after getting in bed and only pop the pill under the tongue when I’m relaxed enough. Otherwise, it not effective.

I found a liquid melatonin on Amazon that let's me dose 0.3mg. I take it 30-60m before and it definitely makes me tired. I still have to go with it though and put myself in bed to sleep; sometimes I end up powering through and end up more awake :d

I use melatonin gummies, which are easily divided to get a sufficiently small does without much work, highly recommended