Is the nine hours all driving time, or does it account for food and fuel stops? Figure on about 2.5-3 hours overall for a couple of food breaks and a couple of additional restroom/fuel breaks. If the nine hours doesn’t include that, now you are looking at up to twelve hours, barring any traffic situations.
As a solo, I would still do that in one day (and did when I evacuated for Milton). As a family with a small child who is borderline potty trained, I might be inclined to break it up more. I would probably leave the evening before I had planned to and go a quarter to a third of the way, stop overnight, and do the rest the following day. So with a potential 12 hour trip, I would drive 4-5 hours and then stop for the night. Doing it this way means you don’t lose a day by splitting the drive over two full days, but also gives you an extra cushion of time on the longer driving day, should you need it. If you decide to make an overnight stop, pack one small bag with just what you need for that stop so you don’t have to get into the rest of your luggage.
If the nine hours does include time for the necessary stops, then I might try to push through in one day, but I would leave early in the morning (no later than six), again, to give a cushion of time at the end of the day and the opportunity for an early night so you can hit the parks fresh on the first day. I would not want to be arriving at Disney after a long driving day, late at night, and planning a full park day the next morning. Being in a car all day can be more tiring that you think.
Whichever you choose, I hope you have a great trip!