As many people have said here, a week or seven days would be overkill.
I love the time system in Majoras Mask, I was hesitant as first but it really grew on me, the fact that you would have to think about managing your time appropriately gave you a sense of urgency. I think three dayswas a perfect balance, you would have enough time to do quest stuff but onecould manipulate time, say if they eanted to slow it down or speed it up. I think that the argument against there not being enough time is quite misunderstood, as you can easily slow down time and explore areas as well as actually completing quests. Then you could just restart after reaching a checkpoint and either advance further or tacke some off plot objectives.
Saying that with three days you did still have that sense of rushing and urgency, to be honest if there was an extra four days wpthis would have defeated the objective that Majoras Mask tried to achieve. Plus there is also the hassle of trying to skip through days just to get to a certain time and this could involve a lot of waiting. One plus I could see from this is that there could have been a lot of room for new quests, side quests and just general change in routines on the days.