You can leave the supers on as long as you like, just expect them to tap into it if you leave it on all winter.
If you have a good strong hive adding 2 or more supers at a time is usually not a problem even if your using fundation. the best rule of thumb is to super before a major honey flow and add enough to see the hive through the flow.
As MB states, with a swarm or a package it is possible to super too early, which is supering before you have enough bees in the hive to cover the frames.