Well just briefly going over it in my mind... say there are 5 potential outcomes for a day, then 5 potential outcomes for each of those outcomes the next day. Then 5 potential outcomes for the previous day's outcomes. That's 5x5x5x5... 5^10 if you will. That's nearly 10 million possible outcomes for 10 days.
Haha, not saying that I'm going that in depth, but I think 10 days could be enough time to have some fun and have some sort of storyline between whatever characters the player comes across.
Edit 1: And yeah, Majora's Mask is a great game, despite how annoying it was to live 1 day 24931289 times.
And I'm thinking that if a player really wanted to, he could just sit there for 10 days picking flowers, if he really wanted to.