If you've ever done any spackling around the house you never quite know when to sand. There is a compound out now that is pre-made and works like a charm.
You apply it to the area you need to spackle; in this case it was a hole from where I removed a recessed toilet paper holder(K needs a fancy schmancy brushed bronze one to match the light fixture-yes, dear).
The cool thing about this stuff is that it goes on pink, and as it dries it turns white. As you can see below, it is not quite fully dried so no use in trying to sand it down yet.
Just wait until you have full on white and you're good to go. It's called Dry Time Indicator Spackling by DAP.