For TS reservations we were only able to make online dining ADRs for our first resort reservation. We had to call to make the ADRs for the second part of our stay. Sometimes you have to call more than once to get a CM who will make the reservations for the second resort stay.
Also, if your total stay is longer than 10 days, you can only make reservations for 180 + 10 days at first and will have to wait until the next day to make reservations for the 11th day, the following for the 12th, etc.