Creatine is one of the few supplements that I can say has noticeable immediate difference on or off. Without it, my recoveries take longer and I have to back down workouts to 4-5 days a week.
5mg a day... time doesn't seem to make a difference but I take pre workout. No hair loss or other side effects.
DHT appears to drive hair-loss in genetically-predisposed men: https://www.ncbi.nlm.nih.gov/books/NBK278957/
Propecia's mechanism of action to stop/reverse male pattern baldness is to block the conversion of testosterone into DHT: https://www.ncbi.nlm.nih.gov/books/NBK513329/
There is not a proven pathway from creatine to hairloss, but if you are genetically predisposed to male pattern baldness then increasing the amount of DHT in your system via creatine supplementation may contribute to further hair loss insofar as DHT drives hair loss for certain men.