There is a clock that starts ticking when you check into your training squadron. It doesn’t stop.
If you go over the max allowed days - there are 3 tiers, if i recall correctly - the commodore is directed to attrite you.
@squorch2 is correct. There is a guy who was attrited from VT-86 last year because he broke his collar bone for the second time while in training. Your job as a SNA or SNFO is to train. If you can't train in the prescribed time frame they will boot you. That is the current environment regardless of how it was years ago or how it may be years in the future. The training command is fluid; they change required NSS, number of down/SODs/Pink Sheets, need to graduate numbers, etc. all the time. It isn't fair, but it is the reality.