USUALLY, with daily turnout, I don't have to fully strip a stall for one week. BUT, we live in IL, which used to be a swamp and is often cold and damp in the winter, so sometimes I have to replace it sooner.
Don't look down on straw. Sometimes we have dropped down to a low of -20 degrees F in January. When that happens my horses really appreciate 3-4 flakes of straw to lay to radiate their heat back on them at 5-6 am, when the radiational cooling, on a clear, cold, night, is the worst.
You need to watch to see how each horse decides to use his stall for placement of the pine pellets and where you pile on shavings and maybe use some straw.
I just bought 10 bales of straw, and it may last the whole winter. My supplier has more, if I need it, too. =D