What is required to happen on that date is the party (not the candidate) provides the state with a list of names that are to appear on the primary ballot.
In many states signatures are required to get on the ballot. That is what is required in Iowa. We hold a caucus so it isn’t necessary for President, but if we had a primary it would be.
Signatures take time and ground game. You can’t just announce a day before and get on the ballot. A month is a minimum safe margin IMO.
In the end it’s a hard delegate count that wins. All the strategy in the world isn’t going to change that. It’s time for everyone to crap or get off the pot.