Quite a few sources recommend not drinking any alcohol within 6 hours of taking 5-HTP. But there is little information on the interaction of 5-HTP and alcohol. It seems a few people said they had a bad reaction, so some sources started recommending avoiding alcohol while taking 5-HTP. Most of these reports were from people taking large doses of 5-HTP and drinking large quantities of alcohol close together though. I would assume it should generally be pretty safe to take your 5-HTP in the morning and then drink at night, I've certainly done it without problem, but I would start off drinking a smaller amount than usual to be on the safe side. I don't know how much 5-HTP you are taking, how it affects you, or how much alcohol you normally drink.
Niacin can cause flushing and itchiness. Consuming alcohol close to when you took the niacin might possibly make those side effects worse.
In general it is best to hold off on drinking for at least 4 hours after taking your vitamins. Alcohol might interfere with absorption, cause nausea, or it might be hard on your liver to take them at the same time as alcohol or to take large amounts of certain vitamins while drinking or if you drink frequently. If you are just taking a normal multi-vitamin and not massive doses of these vitamins, you take the vitamins in the morning and drink at night, you are otherwise healthy and don't have any liver problems, and you only drink on weekends I don't foresee it being a problem.
