I don't believe so. I do know of appointments happening later, in which case I think they will give you another deadline. There are a lot of factors involved, including those who decline appointments, etc. TL;DR - appointments should still come out after 15 April
I suspect the time to accept appointments will shorten as offers are made later in the process (closer to R-day). You still have to do paperwork once you accept and WP has to time to process that paperwork.