Well actually you can upload your game at any time after the jam started, and update your builds until the deadline, so there's really no reason to wait for the last minute, and thus in theory no need for a grace period. One should always plan to have the game published at least 2 hours before the deadline, to be able to fix any pending issues with publishing.

That said, Max here did a great job helping those who missed the deadline, so that's cool :)