I think whether the defense had it on the 13th, when they were attempting to depose Witness 8, author of the letter, or whether they didn't get it until the 15th, perhaps in time to at least ask Sybrina about it, matters.
The reason I think it doesn't matter as to Witness 8, is that O'Mara is not done deposing Witness 8. If I'm in error on that point, then I agree, withholding the letter until after Witness 8 has been deposed would be a big deal.
Assuming the letter has been know to and in the possession of the state for a year, the delay in turnover is part of the pattern of delay that O'Mara is requesting sanctions for. My opinion is that the prosecution is improvidently brought in the first place, and it does not surprise me to see the prosecution acting unprofessionally. Same for the bench. Not that I think all Florida courts operate this way, but whenever I've been looking, they do. Maybe it's my fault
I'm also reminded of O'Mara's request that some of the detective and police witnesses be put under a court gag order to not talk amongst themselves about the case or their depositions. I think a similar gag order would be prudent toward Witness 8.