180+10 means that if you have a on-site resort reservation (
DVC or not) that when you are 180 days out from the FIRST day of your trip, you can then book ADRs for Days 1 through 10 of your trip (assuming your trip is 10 days long). This includes all the people in your party. (I am not sure if you can book parties larger than your group, but I think you can do that as well.)
Someone that does NOT have an on-site room booked (DVC or not) could call on March 1st and book August 28th, but NOT beyond.
In my case, that meant on March 1st I could book dining reservations for August 28th (180 days from 3/1) through September 3rd (186 days from 3/1) because that was the span of my reservation.
If I was staying LONGER than 10 days on one reservation (say 14 days through September 10th), then I would only be able to book through the first 10 days on 3/1. I would have to wait until 3/2 to book the 11th day, 3/3 to book the 12th day...etc.
Get it?