I went out on medical in Spring 2017 but prior to that the FAA would allow "Sonata (zaleplon) with certain restrictions. I used it for early wakeup's since I was a "night owl". I'll paste a description below, I did sometimes wakeup with a vengeance after about 4 hours but overall it was better than nothing. I have heard that melatonin only works via a "placebo" effect, I don't know if that's still considered true or not.
Sonata (zaleplon): It reduces the average time it takes to fall asleep by 10 minutes. Unfortunately, it is metabolized quickly and may wear off within 4 hours. This may make it attractive for awakenings that occur in the night, however.
OK, I got curious and checked the FAA's Guide for AME's. It says 12 hours from taking zaleplon to flying. Didn't used to be that way. It's still the most lenient of all prescription sleep aids thou. I'll link the website with the waiting times for all prescription sleep aids:
https://www.faa.gov/about/office_org...arm/sleepaids/