When running in "steady state" mode the simulation will continue until all user goals have achieved convergence. I'm not sure exactly what happens if the user does not specify any goals. The software automatically determines convergence criteria but you can manually adjust these values.
In "transient" mode you can set your time step and simulation duration.
You can set your own goals to act as convergence criteria. If none are set, it is my understanding it runs for a set number of travels, 4 travels in most cases I have observed. The number of travels may vary depending on the analysis options chosen.