These 'school trips' are surprising, I went to TP with my mates from Uni in April, and there were two large groups of kids tearing through Pizza Hut and being a nuisance. We couldn't tell wether they were from a school or some sort of club or something, but it was a random wednesday (i.e a school day) - not in any half term or holidays, so whenever you seem to go they are there!
From my school days we would visit either Camelot or AT at the start of July, so you may be OK as it's only early June.
You could always give TP a call as they will of course know of all the schools planning a visit and when!