I used to leave them loaded numerous days but after a few misfires, I went to shooting it off, cleaning it, and loading fresh every morning.
I think a lot has to do with the climate we hunt in, and weather conditions we encounter. Also the kind of rifle. For instance an inline is more forgiving in the ignition department the say a flintlock or percussion cap rifle. But I always say, do it as long as you are comfortable with the rifle working fine the next day. If you have doubts, clear it and clean it.