Can I change the simulation time per generation after I start the simulation?

You can change this option at any point in time during the running simulation from the pause screen. The new value will apply starting with the next generation to be simulated.

For example, if you are in the middle of simulating batch 2/5 and you change the simulation time from 10s to 20s, batches 2-5 will still have to finish simulating with 10s before the time is actually changed.