I think no matter how hard we try, it is very hard to leave a small footprint when staying with a friend. I think one or two days is ideal - you have time to talk, laugh and not enough time to get on each others nerves.
Years ago we had houseguests for 9 days - we wanted them to leave so badly but they just would not go. The only reason they finally left is that my husband's parents were scheduled to visit. The houseguests were inconsiderate, took 1/2 hour showers and never once purchased any food. It affected our feelings about them.
I was young then and couldn't bring myself to say anything. At my age now, 60, I would sit them down and make a plan. Live and learn.