For me, when I take melatonin, I feel sleepy within about half an hour, and if I don't go to sleep then, the sleepiness will pass and the melatonin would be ine

For me, when I take melatonin, I feel sleepy within about half an hour, and if I don't go to sleep then, the sleepiness will pass and the melatonin would be ineffective. So I take it about half an hour before bedtime so that I am in bed within the effectiveness window.