If you’re going for runtime in a single-use, you’re going to want to consult the specific manual/guide that came with your unit. However, if you’re talking about a total runtime over the course of its life, that’s going to depend on a few things.
As a rule of thumb, especially if you want to increase the life of your RV generator, you should stop it within thirty minutes of the maximum allowed runtime. This is going to preserve it for future use. Certain Honda RV generator users have had their models for over eleven years, and counting. If you take care of them, they’ll last you for ages.