Most of the restaurants have been 180 days out.
Disney is in the process of changing its reservation system. Right now, you can only book restaurant reservations up to Feb 22 (or 21), so about 6 months out. At one point, they said they were changing from 180 to 90 during this period (except for a few things that stayed at 180), but honestly I can't keep track anymore!
Supposedly, later in the fall (?), the new system will be up and running -- not sure if they will be doing 180 days or something different at that point.
For a May trip, even at 180 days, you won't be able to book until November sometime, so I'd just keep an eye out here as that time gets closer to see what's going on.