yea you rlly cant put in 2 weeks if you don't have the FINSEL by then. You just have to give it to your employer. I think legally even though its not 2 weeks notice they still cant fire you.
USERRA protects you from employer retaliation if you're applying for a position in the armed forces. I only really found out about it bc I used to be a construction inspector and reading the required posters on the contractors' bulletin boards was part of my job lol
USERRA
There are a lot of protections in place tho, it's a good read if you have time