if you don't intend to turn it off, turn off fast boot and then windows might be less inclined to optimist your loading order for programs. As it doesn't know you don't intend to turn it off, it tries to organize your drives so that they will boot in a way that the programs you use the most are first. You can't do much to stop that, its done auto by system & compressed memory.
After a few weeks it should stop using your down time for its maintenance.
Its not like it stops you doing anything as it stops its busy work as soon as you move the mouse. If its your AV, you can normally go into the actual app and stop the scan or pause it if you want. Best to schedule scans for hours you not using pc since its always on.