This advice comes from a doctor who wrote a book that I have on my shelf:
5HTP can be taken day or night. 50mg in the morning and 50-100mg at bedtime raises serotonin levels.
It’s a good sleep aid when taken at night, one hour before bedtime. If daytime use makes you drowsy, take the entire dose (50-200mg) at bedtime. If it’s too activating, try L-typtophan instead.
Try taking it at night and see what it does to you. Report back, because I’m curious!