Hiya, Jacqueline! Welcome, and thank you for your question.
As you probably know, you can make
dining reservations for
Walt Disney World restaurants as early as 60 days prior to your arrival, with a bonus of making them for up to 10 days if you are staying at a
Disney Resorts Collection hotel. But you can book any of the restaurants on the same day - even up to the time you want to dine - as long as there is availability.
If you are booking on the day of and using your
My Disney Experience app, there's no particular time you can check for an available table. Once you hit that 60-day mark, you can check for dining reservations online or on your app any time, day or night. On your app, you'll click the plus sign at the bottom of your screen, and the first button that appears at the top is Check Dining Availability. You'll put in your party size and then click on the date you wish to dine. If you are doing same day, you don't even have to specify a time - you can just click the "Now" button. It will bring up restaurants near you with availability immediately.
Some restaurants are easier to get reservations for, while others are a challenge. I recommend if you are trying to get a more difficult reservation, like for a character meal, you keep checking for availability. People change plans and cancel reservations all the time, and you might luck into one.
Good luck, Jacqueline!
Anna