This class is responsible for calculating the time step of each tick of the engine during a Movie Render Queue render using a linear strategy - the number of temporal sub-samples is read from the graph for each output frame, and we then take the time the shutter is open and break it into that many sub-samples. Time always advances forward until we reach the end of the range of time we wish to render. This is useful for deferred rendering (where we have a small number of temporal sub-samples and no feedback mechanism for measuring noise in the final image) but is less useful for Path Traced images which have a varying amount of noise (and thus want a varying amount of samples) based on their content.