Filler question

Im starting the bodywork on my coupe, starting at the back Im working out the dents and imperfections...some of the previous metal work is terrible and is gonna need filler no matter what.
My question is how long can you leave filler on before you actually prime/seal the whole car?

 

I tried to never leave the shop without applying primer to keep the rust from forming.

 

Unless it's in a climate controlled building I wouldn't leave it far more than a few days. Even then, I'd try not to...I'd at least prime the filled parts.