Hi Alex,
The short answer is that WaterGEMS inserts intermediate time steps as required so that controls are properly modeled. For example, if your WaterGEMS calculation time step is 1 hr, but you have a tank that will empty to a 'pump on' level at 23 mins after the start of the simulation, then WaterGEMS knows it needs to solve the network at that intermediate timestep (time = 23 mins) and turn the pump on. So after you compute you might see results from time 0:00 (first 'standard' timestep - pump is off), 0:23 ('intermediate' timestep - pump is now on), 1:00 (2nd 'standard' timestep), etc. WaterGEMS does this by keeping track of tank outflow rates, levels, etc. and calculating the time when a control will be triggered.
There are some slight differences between how logical controls and simple controls are evaluated, but that's probably going into more detail than you are looking for at the moment. Please let me know if you would like more info.
Regards,
Mal Sharkey
Product Manager Bentley