Not sure on the timetable in your area but the last two years here in WI I believe I had gotten nesting Blues after a failed first attempt due to the timing of them nesting here in my yard. Last year they first started a nest the end of May, babies fledged July 3rd. The year before that the pair I had didn't start nesting here in my yard until later in June. Usually nesting starts here in mid to late April. So you could still get a nesting if they have a failed nesting elsewhere as they will look for a new nestbox. Good luck!

Donna

Never too late! You never know when a bluebird (or other native cavity nester) needs a home. Anything can happen, a mate is lost, HOSP take over, nestbox or tree gets removed or falls down, nest failure or babies die, predators, competitors, the list goes on and on. Bluebirds are always scouting for homes for now or later, and roosting sites to sleep in or take shelter from bad weather. They will remember.
Meanwhile, be sure your nestbox setup is safe for them. Visit http://www.sialis.org/windowstrikes.htm for tons of info.
BlueBars