Absolutely! ADRs can be made by anyone, regardless of where you're staying. The only advantage to staying in a resort is you can book 180 days in advance of your arrival date for your whole stay [up to ten days] if you have a confirmed reservation.
But how far in advance can you make ADRs if you're NOT staying on-site? I think that's the question. Personally, I didn't know staying on-site was a pre-req for making reservations. I figured there must be locals who make reservations for meals in Disney resorts
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