The clock in Majora's Mask wasn't there to provide time pressure during the regular Zelda dungeoneering. That's the part of the formula that rarely gets tinkered with, and MM had relatively little of it.
The clock was there to provide a Groundhog Day-like structure and a more genuine "approaching apocalypse" atmosphere. If you don't act, the world really does end. And by the end of the game, you've not just saved the world, but got to know everybody in the game world and made a difference in their lives. It was much more emotional game than other Zeldas, especially in comparison with its predecessor, Ocarina Of Time, which is what it had to measure up to.
The clock was there to provide a Groundhog Day-like structure and a more genuine "approaching apocalypse" atmosphere. If you don't act, the world really does end. And by the end of the game, you've not just saved the world, but got to know everybody in the game world and made a difference in their lives. It was much more emotional game than other Zeldas, especially in comparison with its predecessor, Ocarina Of Time, which is what it had to measure up to.