On my 180 day out mark I was logged into the Disney site before 6:00 a.m. EST, and precisely at 6:00 a.m. I was able to start booking ADRs. After I linked my resort reservation to the first ADR I was making, I was able to make ADRs up to 10 days out (even though we're only staying on site for 8 days).
I got everything I wanted. I found that sometimes I would input a desired time and the reservation system would come back suggesting another time before or after my desired time. If I didn't like the suggested times, I would try again with an earlier or later time, and almost always eventually the system would come back up offering the time I originally requested. So when people say they couldn't get the time they wanted for a given meal, I always wonder if they tried requesting any different times.
The whole process was really easy. Have a great time!