Day One
At any time from 8:00 A.M to 1:00 P.M, visit the Mayor's
office. Talk to the Mayor's Wife/Lady Aroma/Kafei's Mom and
tell her you'll look for her son to get the Mask of
Kafei. (If she doesn't give it to you the first time,
try talking to everybody in the room, or leave the office
and talk to her again.)
Go to the Stockpot Inn at 2:00 P.M. The postman will arrive, give Anju a letter, then leave. When he's gone, talk to Anju and tell her you have a reservation. She's feeling so hazy that she'll automatically give you the inn key, letting you access the inn after it closes. (By the by, your room contains a silver rupee that recharges everytime you warp back to day one, so if you need some pocket cash...) After you have your key, put on Kafei's mask and talk to her again. She'll gasp, then ask you to see her in the kitchen at 11:30.
Be true to your word: head to the kitchen (in the back hallway of the inn) by 11:00 P.M and wait for Anju's entrance. Say "yes" to her plea for help to get a letter to Kafei. Once the screen is done fading to white, run out and pop the letter into the nearest mailbox.
Day Two
Rather than wait for the Postman, just be at the Laundry Pool by
2:00 P.M. He arrives roughly at three; make sure you're on the
path that leads to Kafei's door when he does. The Postman will
ring the bell, causing Kafei to exit his house and rush towards the
mailbox. While he's gone, hurry into his house and run upstairs
before he comes back and locks you out, forcing you to start the
quest over again. (Believe me, you have MORE than enough time.)
Kafei will return in a moment or so; Talk to him to hear his story. He'll give you his pendant and ask you to deliver it to his fiance, but before you do, speak to him again to be allowed a neat little peak into the Curiosity Shop. Afterwards, give Anju the pendant and wait the night out...
Day Three
Day three of this sidequest has multiple options, meaning that
you'll need to redo the quest three times to get all of the
possible items. At any rate, the last option can't be done
until you've reached a certain point in the game.
Empty bottle: Head back to Kafei's house at 6:00 P.M. The man from the shop will be there, and he'll give you two things: express mail and the Keaton Mask. The mask is yours to keep, but the express mail is the doubling part. For the bottle, take the express mail to the Milk Bar immediately, put on Kafei's mask, and give it to Lady Aroma.
Postman's Hat: Certainly not an important item, but it's cute, and you need all of the masks to beat the game. Do the same thing you would do to get the empty bottle, only DON'T give the mail to Lady Aroma. Instead, give it to the Postman. Follow him into the Milk Bar to watch the delivery, then follow him back out. He'll give you his hat before fleeing from Clocktown.
The Couples' Mask: I can't find any use for it, but you'll get to watch a cute cinematic and sneak into Sakon's home without using glitches! YAY! Oh, but it IS a little tricky...warp to Ikana village by 5:00 P.M and go up to Sakon's Hideout. See those two square rocks slanted against eachother? You'll see a dash of purple behind them if you get close, so be sure to run around and talk to Kafei. He'll say a few things, and when he's done, whip out your ocarina and play the Song of Time Compression. [Down, A, Right, Down, A, Right.] It sounds pointless, but believe me, you'll want it during this.
Stay hidden behind the rock with Kafei, because Sakon will start coming (*ahem* PRANCING!) up the hill at 6:00, and at 7 on the dot, he opens the door to his hideout. Follow Kafei in through the entrance, then go into the first door. Your partner will accidentally start the conveyer belt, but ignore Chat's whining and step on the switch.
Now, here's where we Kafei fans have a wild time: you get to be Kafei! Basically, you need to step on the blue switch to open Link's door. The first puzzle is easy: push the left block onto the switch. Link's part in this is to defeat the baddies as fast as he can-the Babbas are easy, and I've found that the Wolfos' are weak in their backs, so do a backflip when they pause in front of you-and therefore open another door for Kafei. The second puzzle is even easier: just run our mastermind onto the blue switch, as hitting the others does nothing. Make Link fight the monsters and get ready for the "trick" room.
It's easy to get stuck on the third and final puzzle because you're in such a hurry. IGNORE the blue switch for now and move the blocks out of the doorway before hitting the switch, or both of our heros will be stuck! After that, it's easy as cake: get both men (boys?) to stand on the switches in the next room, thereby stopping the conveyer belt.
Kafei will run back to Clocktown with the Sun's Mask while you take the easy route: warping. Warp to Clocktown and hurry to the Stock Pot Inn (you don't have much time!), then go up the stairs and enter the Employee's Only room (the first room). Anju is waiting there devotedly. When about 2 or 3 hours are left, Kafei will come running in. Enjoy the adorable cinematic, then accept their gift of The Couples' Mask. Quick! Take the ocarina out again and warp back to day one.