You did a good job comparing the claim to a credible source like The New York Times, but I’d be a bit more cautious with the conclusion. If Iran publicly denied that negotiations were happening, that makes the “successful negotiations” part of the claim questionable, even if Donald Trump said talks were going well. Also, the difference between 5 days and around 10–12 days isn’t minor and suggests the claim isn’t fully accurate, so instead of calling it mostly true it would be more accurate to say it is partly true but misleading since key details like the length of the pause and whether negotiations were actually happening do not fully match up.