Out of interest, what (vaguely) is the amount of time you need between maintenance refreshes?

It really depends on the state of the screen. It's easier with reading PDFs, for instance, when you can get away with a full refresh on page turns.

Versus someone drawing on the screen with a lot of zooming and panning. People with the tablet would notice that when they stop a series of these actions that were back to back, the screen will "clean" itself after about 5 seconds of idleness.