Funny, I received a notification about this question, I actually work at San Angel Inn. You can make a reservation 6 months ahead of time if you are stay in Disney property or 2 months if you are not, by using the app. Take in mind you have to do it exactly 60 days before you come in, to be able to see availability. Or make a reservation the same day for cancellations on the Disney App. We normally take walk in before 11:30am. We honor your reservation if late. Hope this helps a lot!
If you download the disney app you can make it in there. Click the + then check dining availability, select party size, time of day, then you can see if it's available. Calling might be easier but could take longer depending on how busy they are.
There is a phone number on the page. You can probably call and make the reservation. When I went they had a limited amount of space for walk-ins.
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