IF you have a darkroom, you can develop different films in the same tank at the same time, for different developing times. Here is what you do. You fill the tank with developer and leave it in the sink. You then load your film, keeping track of what film is what. When you start, you put the film needing the longest time in the tank, put on the lid, and start the timer..
Lets say you have a film that requires 10 minutes developing and one that requires 8 minutes developing. In the dark, with your glow-in-the-dark timer you watch the time and after 2 minutes you open the tank and plop in the 8 minute film. If then, all the film is in the tank, you can turn on the light and proceed normally.