It might very well come on April 8th, since malware authors who find exploits in the period leading up to that date would wisely wait until right after the no-more-patching cliff to release their new 0days.
Considering how many Firefox flaws were saved up for the recent hackathon (since the rewards are 6x what Mozilla usually pays as a bounty), I'm betting on at least a couple critical ones being unleashed the day after, though it may take some time for them to be caught.
