It all depends on your preference in the strength and taste of your wine, one month is adequate you can always add more down the road...........you should be looking for a PH reading of around 4/4.5 to carry out the robust taste of this style wine. at least that would be my input.
Started this on 1/10/15 bottled last night.
Had glass leftover, this Amarone is going to be good! Only 7 months in and love the mouthfeel, can only imagine how the flavors are going to improve over the next year or so.