I would recommend once you do decrease the lighting time, cut back to 21 hours for a week, then keep it at 18 for a month or so. You can decrease to either 15 or 12 in the weeks leading up to outdoor planting, depending on your preference. Daylight max in July is about 15 hours in most areas, so I would keep it around that mark. If you don't have your lights on a timer, I highly recommend one of the dial type ones from Menard's or Home Depot, Lowes, etc. They are less than $10 and usually work pretty well.
I have my timers set on 15/9 for the C.Chinense/Baccatum/Frutescens, since they grow more slowly and over a longer period of time. I then have my other room, which houses my wild species, C.Annuum and C.Pubescens, on a 14/10 timer. My motivation for this light cycle this early is because I don't want an enormous power bill. I have 91 pepper plants, a gourd plant, 12 strawberry plants, and 4 tomato plants going, so I have 2 grow rooms. Next year, I am definitely growing less, but now that I've committed to these little ones, I will be sticking it out until the end! Only one grow room next year!
Good luck with your season, and welcome to the boards!