Donvier Ice Cream Maker - why stirring only every 2 minutes?
I have had that icecream maker for decades. I never had a problem with ice crystals following their directives. Since you don't need to churn it continuously, they tell you there's no need to. The mix needs some time in contact with the walls to get cold. 

If you have kids, it will get stirred more often than the instructions say. But that tends to work out ok too. It's pretty forgiving all around.