There's a reason each of the Tattered Ability effects only come in to play if you roll a single number.
Yes, because effects that result from alterations to the fundamental essence of your being frequently wear off within one month to a year.Or you could make all the effects have a d12 month duration or so.
Now that I got the sarcasm out of my system, there's a metagame reason for not assigning durations of 1-12 months. How many DMs actually keep track of in-game time? And how likely is it that by the time the duration ends, both the DM and the players will have forgotten that it has a duration in the first place?