The minimum mining time never had anything to do with the scoring system, it was only to make sure we didn't switch too often.
Ok, but wouldn't be better to have a minimum difference instead of a minimum mining time. Let's say we start mining a coin that has a minimum mining time of 10 minutes but soon thereafter an other coin's profitability jumps up to triple the current coin's profitability. Wouldn't it be best to switch to that coin immediately instead of "wasting" 10 minutes on the lower profitability coin? A good example is MNC which sees significant peaks in profitability that last less than 10 minutes. Because of the minimum mining time, I think we might sometimes completely miss some of these peaks. Maybe you could combine a minimum mining time with a minimum difference. For example, stay on current coin a minimum 10 minutes unless another coin is more than 50% more profitable. After 10 minutes switch to the next most profitable coin only if 1-2% more profitable. This may actually reduce the amount of coin switching and increase total profitability.
-Just a suggestion-
By the way, your pool keeps getting more and more awesome!
Without giving away too much, there are definitely times where it's more important to move than to stay on a coin for the minimum duration. The script accounts for that.