It is true that most schools do not go to their wait list until after May 1, but it sometimes happens earlier. I recall from last years discussions a bunch of schools went to wl’s before May 1, and a couple days ago someone said that Bates had taken someone off the wl already this year. Don’t count on it by any means, but you can wait to put the deposit down at the school he is accepted to until may 1 or a day or so before… just in case.
Good luck