I think you can start making Advanced Dining Reservations 90 days before your trip. If you have a large group, I would call at 7am on your 90 day mark and have several times that you're willing to accept. If you want some of the more difficult ressies (like Cindy's for breakfast) have back up dates in mind - they go fast!
The above poster was correct in stating that you can make ressies up to 90 days in advance.
Also, even though they are now called Advanced Dining Reservations (ADR's), they still work the same as PS's. That is, you make a "reservation" and you are given a spot in line for a table for your party size. It's not like a table is held for you, as you might expect at other restaurants when you make a reservation.
I wish they'd have just kept the PS name for these. I'd prefer they move to a system where an actual table is held for you for maybe 15-20 minutes after your reservation begins, and in return for this, I'd be happy to give them a card number to "hold it", like they do for HDDR and the Luau. If someone doesn't cancel an ADR within, say, 2 hours of the reservation and fails to show up, a financial penalty could be applied, like it is for HDDR and the Luau. That would discourage much of the multiple ADR's people are making for the same time. Since there's no punishment to keep people from doing this, the only thing stopping them is their conscience, and unfortunately that is often not enough.
You can use the tools on my site to figure out when to call. I just updated the PS Report (PS now stands for Planning Strategy so I can keep the PS on my stuff) to allow for the first day of check-in if you are staying at a Disney operated resort at WDW.
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