The primary will almost certainly be de facto decided by the end of March. There's a good chance it will be de facto over by mid February, if any candidate dominates the early states.
Of the 2467 delegates up, 1250 of them will have been distributed by March 12. Republicans rules on delegate distribution heavily favor the candidate in the lead as well. No primaries/caucuses have been scheduled yet after March 12, but expect the bulk of the remainder to be in the other half of March and all of April.
The primary is all but certain to be over by May 2024.
And I'm sure they're all banking on Trump to win so they can pull the "you can't run a major court trial with a presidential nominee as the defendant" card.
Trump could clench the nomination in March, then get disqualified from running in May. The GOP will have to slap together a quick Desantis, Pence, or Cruz campaign with zero cash, while Trump fights the disqualification in the appellate courts.
An interesting thought, and completely unrelated to the May trial, but it's possible that the upcoming J6 indictment could include certain conspiracy charges that would prohibit holding office if convicted. I think the timing of that trial will be more important.
It's worse: If Trump is the nominee you just know he's going to spend all the campaign dollars on lawyers for his various trials. He'll do his usual tour of the states doing his rallies but exactly zero dollars will make their way to downstream candidates. He's going to cost them the presidency, the house, and the senate.