If you ask me... P&P Party is going to be a "year round" event with exception to the MNSSHP and MVMCP. It could just mean that we don't see "as many" parties during more popular weeks/dates.
Last Year's dates were:
August 15, 18, 21, 24, 28, 31 and September 3 with MNSSHP not stating till the 14th.
This year's MNSSHP dates are not even out yet... but rumored to start on September 5th; yet that's the same night as confirmed Night of Joy, so most likely the party won't start till that following friday, September 12th. So far it seems they're on track to follow the same trend as last year.
When we went on 3/11... every other night at the Magic Kingdom for our week of travel had closing at 11pm plus the occassional EMH night; P&P was offered 2 nights of our trip.
If they're offering it during the entire Spring Break season, with some weeks reaching 9 and 10 on the crowd calender... I don't see why a June or July would be any different.