IME in the Northeast, flowering will start around the 2nd week of August, so count from Aug 15th for flowering as a general rule of thumb. If you want a month and a half of veg, go for July 1st start date, and you'll have smaller sized plants that should do just fine. If height is an issue, I'd top your plants around August 7th, as this will slightly slow the stretch down a bit. I've seen 3 foot plants with a bit of Sativa in em go to 9 feet by harvest time, so keep this in mind depending on genetics.
An 8 week flowerer, I'd imagine will be ready 1st or 2nd week of october. Also, if mostly indica, be aware of late season rains. If you have daily access to your plants, try to (gently) shake off an overnight rain shower in the mornings to lessen the chance of mold and bud rot once they start bulking up.