The simulator contains a single laser to generate the target spot representing the clay. When you select simultaneous doubles the simulator displays the first target and, when you shoot, it immediately switches the laser to follow the path of the second target. So, if you are 1 second into the flight of the first target when you shoot, DryFire will pick up from 1 second into the flight of the second. On Skeet Station 4 your left-to-right high crosser will switch immediately to the right-to-left low crosser.
“On-report” doubles are obviously no problem – as soon as you fire at the first target DryFire will release the second.
When you have taken both shots (or failed to take both shots!) DryFire will show you the shot location for both targets.