I believe a 90-day window for TSA or PRIA or similar exists regarding class date. In other words, if they "assign you" a class date, then you later say, hey I need to attend a later class, something came up, that causes a lot of issues.
Probably saying what previous posters said, but whatever your availability date, make that for sure 100% that you can comply with that date.
I would be at every job fair that exists 12 months or sooner, prior to your retirement. With "apps submitted" also by then.
Good Luck