5 minutes is probably too short. You don't want to be in a situation where you mine for 5 minutes without a block being found, then move on. I would say someplace between 15-25 minutes would be good, depending on where you mine, algorithms, and coins. Also if you have alot of algos, and pools selected, a longer switching period lowers the chances of something going wrong if you can't always monitor your rigs 24/7.