It all depends on the beer. Of course, all beers need enough time to carb up. On top of that, there is no real set formula except for the higher ABV, the longer it will take to really be in it's prime. A 15% barley wine will take longer than a 7% stout, obviously. The same goes for your IPA. The hops will fade with time but if you are making a huge, kick ass IPA then you should accommodate for the aging by having more aroma hops.