Airlines want you checked-in 3hrs before an international flight, though physically going through security and getting to the gate can vary wildly from 30-60 minutes (security+tram+walking). On a Saturday, you'd probably skew more on the higher end.
You can probably shave some airport time if your airline offers Resort Airline Check-In with Disney (it's a very small list)
then at least the bags can already be checked and on their way, and when you get to the airport you just go right to security.
Rental car return and then the walk to the terminal is probably a 15-20+ minute process. Pull into the garage, get sent in circles, wait for staff to check the car, and THEN you start walking.
The drive to the airport could be 30 minutes on a good day, but if you're on the far end of property or trying to drive on I-4 or past Disney Springs on a Saturday, that can double or even triple. Don't forget grabbing gas too. In most cases you can fill up at a Speedway on Disney property and the needle won't have moved by the time you get to the airport, but there is a slight risk there. I'd rather overfill than have to stop near the airport. Time saving option is prepaying for fuel with the rental company, though you'd want to be Kramering it to the airport.
I'd aim for leaving 10am. It's early enough that you could be lucky and get to the airport, car returned, and in security line shortly after 11, which leaves you tons of time to make it to the gate, even on a bad day. Add a buffer if there's slower members (young kids, elderly, etc.) in your party.