Fermentation schedule for New England IPA?

Hello I am going to brew this New England IPA recipe from may-June 2017 BYO article. But i am little confused about the way the Arthur of the recipe say to ferment it. He say to start fermentation at 64f an allowing the temperature to rise naturally as fermentation progresses. Ok I know I pitch the yeast at 64f an start the fermentation at 64f but how long would one want to hold it at the 64f before allowing it to naturally rise like the recipe state?

I usually wait until it slows down. Couple days or so or longer if you want. I’ve let it ferment there for the duration the only thing warming it up does is speed it along. It makes sense if using a swamp cooler to just stop adding ice . Of course you want to keep it from getting to warm