In my experience (admittedly a few years old at this point), it'll work like this: Let's say today is 60 days prior to your check-in day. You are able to make ADRs for check-in day plus 10 more. Then, tomorrow, you'll be able to make ADRs for the next day of your reservation. And then the day after that, you'll be able to make ADRs for the next day. And so on.
This is assuming you have a single reservation at a Disney resort and not a split stay.
I hope that helps!