If you mean one Harvest Moon day it is impossible. The requirements to get married are:
Have a Red Heart
See all four Heart Events
Upgrade your house twice
Buy the Large Bed
Rescue at least 60 Harvest Sprites
Buy and Propose with the Blue Feather
Even if you cheat for money, affection, and sprites you can not see all her Heart Events in one day. And It takes a few days to upgrade your house and for the Large Bed to be delivered.
Make sure it is not on a Wednesday and must not be a rainy day. >.< bx
give her chocolate and wine every day and if you a harvest sprite and muffy to like you buy ten drinks at the blue bar for five nights and you get her to like you and you get a harvest sprite... hope ive helped...
Take wine to her every day, It improves her affection for you by 500. And talk to her twice a day.
That means your character and Muffy are engaged. The two of you will get married on the first day of the second year. It doesn't matter when you proposed, that it always the day the wedding happens.
Any gift that she likes will work. The gift just has a much bigger effect than it would on a normal day.
Keep giving her presents and things she likes every day, and dont forget to talk to her every day as well.
try giving her presents every day and make sure her affection towards you is high eventually she'll become pregnant all on her own
when her heart is yellow, in summer, on a sunny day, exit your farm house from 9am - 12pm and she should ask you out :) say yes to going out on a date.
If she is not at the festival, you will not be able to find her! All houses are locked in order for the celebration and they do not leave their houses. It is annoying, but if you are like me you will be able to see why!
If you mean marrying her, you keep giving her flowers every day until she has four hearts for you. (you can check this in that plant in the Blue Bar) You then propose to her with the Blue Feather when she isn't working.
There is no day you have to get married. In Harvest Moon DS you can get married whenever you want.
If Muffy won't marry you there must be a requirement you haven't completed. Here are the all requirements needed to get married: Have a Red Heart with the girl See all four of her Heart Events Upgrade your house twice Buy the Big Bed Find at least 60 Harvest Sprites Buy the Blue Feather Make sure you complete all of those before you propose again.