I remember a similar (but less serious) situation in which I went 2.5 yrs with 0 vacation.
I was feeling pretty much beat and close to burned out so I scheduled a vacation outside of the country having basically the max number of PTO days an employee can gather. Told my manager of my plans and he passive aggressively told me that sure, you can take PTO... the project is on fire and we'll launch next month but sure, you go on your vacation.
Did not go because I was genuinely scared about my career.
Project got pushed another two months. Tried to do the same, same result. Got pushed back again two months. And I was still there, working my ass off.
Rewards for that year were mediocre at best, although I worked my ass off.
What I learned from that is the fact that work never ever ends. There is no 'perfect' time for leaving. Even after launch, the team may need the original developers to fight fires all day and patch production to keep things running especially if the project was a death march or if the schedule was pushed back a couple of times.
Leave, try your best to not burn bridges and be honest with the current employer.