trims

I would say that a month and a half should do it. I don't think waiting longer is a good idea. But I guess it depends on your styling routine. If you put heat on your hair alot I think you should trim more often. But you don't have to trim alot off. Maybe about 1/8 of an inch should be enough. But if your hair is extra healthy and you don't use alot of heat or have very little to no breakage you may be able to hold out longer since you are trying to grow out your hair. But a month and a half suits the adverage person.