In theory, you can book DLP dining up to one year in advance if you are staying onsite. However one of DLP's "fun" operational quirks is that it doesn't seem to actually open up for bookings on a particular schedule.
For my 2022 trip, I booked my hotel a few months in advance and was able to book dining right away. For my 2023 trip, we're 11 months out and I'm just getting an "oops too early" message despite having an email from DLP telling me I can book dining. So now I'm just checking every few days to see if anything has changed!