You’re allowed to hold onto one acceptance (PTE should usually be indicated but seems this is school specific) and all your waitlists.If Wayne probably isn't going to give out Acceptances until May 2nd and beyond, how does it work with only being able to have 1 Acceptance after April 30th?
If given an acceptance off the waitlist, I believe you’re bound by the timeframe of the offering school to accept their offer (both via their portal/email and the CYMS tool) and submit withdrawal to the other institution (or decline the acceptance altogether I guess). Not sure what exactly that timeframe is but this late in the game it’s usually a couple days.
To more directly address your question, you usually have a couple days to hold onto two acceptances before you incur any penalty.