You'll probably need to call two days in a row. If you have two separate reservation confirmation numbers from Disney, that is. You'll be 180 days out from your first reservation. And the following day you'll be 180 days out from your second reservation. On your second reservation phone call, you'll be able to book the rest of your ADRs.
I know in the past I've had split stays in the same resort for discount purposes, and I had to check out from my first reservation and then check in for my second. Both were done at the same time at the front desk. I had to do this because I was booked as two separate reservations.
