Keep it cool for as long as fermentation takes. After that it doesn't matter too much - although - there may be a tiny bit of fermentable sugars left and warming it up will ferment them out. This is not really a good thing, that little bit of sugar really brings out the apple flavors. Mine often finishes at 1.000 - 1.002ish, but if left warm will go down to 0.997. The difference is amazing, 1.002 tastes dry and appley. 0.997 is tart, not appley, and takes getting used to. Much less of a crowd pleaser.