Well I thought the discussion was referring to him jumping in the race.
This is the first election I’ve ever paid any attention to the nominating rules. They are ridiculously complex, and I hear they get re-written every once in a while to try to nudge the result in the direction the Party thinks it wants. (For example, I heard that the scheduling of the election order, and the number of Florida delegates, were tweaked to favor Jeb, although he flopped so badly it had no effect.)
I think you’re right about deadlines, but those are for the primaries where WE get to vote. The more I hear about the convention rules, the more I think that’s a smaller part of what happens if it’s close, and no one has a majority on the first convention vote.