If the law of averages prevails here why not just make it 20 mins like the big pools? heck even 10? worst case we get some pool hoppers and start catching blocks faster than 5 days....
The shift size isn't going to affect pool hopping, PPLNS is still safe from pool hopping.
Making the shift size extremely small I think would be a bad idea. It would scare the ones that are shocked to see a shift with zero pay. I have to balance between that and the people who think if 10 shifts take 5 days it means they have to mine 5 days with lousy pay before proper pay starts. So I try to keep it somewhere in the middle.