I'm a little worried about what might happen when the three days (72h) are over. It took me a long time to play this hide and seek game and now it's already the night of the second day. What will happen if those three days are over and there is still a mission you need to do? Do you have to do it all over again? I don't hope so though.
Zelda Majora’s Mask 3D – Strategies for First Three Days in Majora’s Mask 3DS
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Related Solutions
No, they haven't included any sort of harder mode in Majora's Mask 3D.
Ocarina of Time Master Quest already existed prior to the 3DS remake, so they choose to include it as a bonus. Majora's Mask 3DS includes a slew of changes to the main game, but sadly no "hard mode" of any kind.
Using the guide you linked to, it looks like the amount of time you need to the mandatory parts of the game is as follows. Note that this is all with time slowed by the Song of Inverted Time.
- Get Song of Soaring: 1.5h
- Go through the swamp and enter Woodfall Temple: 4.0h
- Get Hero's Bow: 3.0h
- Get Bomb Bag, go to Goron Village: 2.0h
- Enter Snowhead Temple: 3.0h
- Get Fire Arrows: 3.0h
That's about 16.5h, or 10:30pm D1. At this point, you can now go to Medigoron and unlock Power Kegs by doing the test (as it requires either Fire Arrows or beating Goht), but it's too late to get Epona, which has to be done before 6:00pm D1. Without Epona, you can't get to Great Bay or Ikana. So basically, in the first cycle (not counting the first one when you're trapped as a Deku), you can't do any better than completing Woodfall and Snowhead.
Looking at the guide again, it takes an entire cycle to complete the second half of all the dungeons: day 1 for Woodfall and Snowhead, day 2 for Great Bay, and day 3 for Stone Tower. Since you had two days to complete all of Woodfall and Snowhead in the previous cycle, we can cross those off, and say that "cycle X" will involve completing the entirety of both Great Bay and Stone Tower. It then takes basically no time at all to enter the Clock Tower and go to the final boss.
Now the question is, can you open the path to both the last two temples in "cycle X"? If X is 3, you lose an hour or two to get Epona. The guide is less helpful here because it doesn't really measure the time needed to get the last two temple songs, but my instinct is "no". It just takes too long to collect the Zora Eggs and collect what's needed for the Gibdo well.
So, I'll say that, if you do count the first one, you need four cycles to finish the game.
Best Answer
On the Final Day, you'll find out what happens after your 72 hours are over. Given how early you are in the game, it's a bit spoiler-y. I'd recommend that you just play through to the Final Day and you'll see what happens after the three days are over. If you can't wait, the next bit is in spoiler text (just mouseover to reveal).
If you're asking about what happens you aren't prepared at the end of your first Final Day, I hope it's not very spoilery to say
rocksthe Moon falls andeveryone diesyou get brought back to the Dawn of the First Day.