5-Htp imo is garbage. The nausea and stomach issues are much harsher than you'd have with SSRI antidepressants. SSRI's are also much more effective. The major downside to SSRI's compared to 5-Htp are of course the sexual problems which will probably be massive. Another issue with 5-Htp is that it only works for a few hours. If you don't have a time released version, have fun dosing every 2 hours!
I always take mine at night. I don't know if it helps me sleep because I take 6 mg of melatonin almost every night, maintain fairly regular/consistent sleep patterns, and seldom have difficulty sleeping.
As for the stomach issues, I've never had any problems, and I feel "extra positive" until about lunchtime the next day. Mine is not a time-released formula. It is supposed to help with sleep, and it is recommended you take it at night. I don't know that a time-released form is desirable.