Hi, Masae! What a cool name, by the way!
If you are not terribly concerned over where you eat or what time you eat, as long as you can line up the hotel and the travel arrangements, there is no reason you can't visit Walt Disney World with only a month's notice! My husband is the king of spontaneity, and he has come home in the past and said, "Let's go to Disney World tomorrow!" I can promise you, regardless of what restaurants are available, I've got the kids packed and in the car, ready to go, at the drop of a hat.
You may encounter some difficulty booking reservations at some of the restaurants. Many dining experiences - like Cinderella's Royal Table, Le Cellier, and Chef Mickey's - will book way in advance. With the free dining promotion that has been so popular, more and more people are opting for sit down meals than ever. If having very specific dining experiences is going to make or break your entire vacation, you may want to consider going at a time when you can plan further ahead. Advanced dining reservations can be made up to 180 days prior to your vacation.
On the other hand, if dining isn't a huge factor, I'd say go! You can go online to see what restaurants are showing availability during your visit by checking out the online dining reservation system, located
HERE. That will help you make your decision.
I hope you have a wonderful time if you decide to go! If it were me, I'd be happy eating counter service just to have the chance to be in Disney World!