Maximum time between primer and paint

Primer is just basically paint so it won’t present any problem as to how long you leave it on before painting. As Tojo said, rushing is the problem.  However, if you do the priming and don’t plan on painting for a long time I’d strongly suggest that after the primer is thoroughly dry to place the model(s) in a box to keep them free from dust and NOT some type of plastic bag or plastic covering as you never know how the plastic will react in long contact with the primer, and or paint for that matter.