This is not exactly what you asked for, but it is very easy to plot the average of a variable (along with the min, max, and quartiles) by applying the Plot Data Over Time filter. (You need the most recent ParaView 5.6 for this to be available.)
If you really need to plot the sum over time, probably the easiest way to do that is to compute the sum with the Python Calculator as previously described, then selecting a single point (or cell) and then apply the Plot Selection Over Time filter.