My guess is either there is actually a regular “Time” node connected somewhere to the right offscreen in that UDK example, or “ImpactTime” is actually being driven by matinee or something so it is changing over time. That switch looks like True is for debug to see the effect loop over and over again.
For what its worth, there is really no “correct” way to do this effect. I can think of a bunch of different approaches so IMO you might as well try building it from scratch if there are issues seeing how the example is built.
I would look at it as two simple problems. Two expanding spheres need to be made, a larger outer sphere and then an inner sphere to cut out the center. The size of each sphere could either by changing by driving radius directly with time, or by “offsetting” the values of the gradient like the UDK example above. Later today if I get a second I’ll try to make a simple example.