We've driven several times from Niagara Falls, and with my brother who's from Hamilton. We have stopped in Columbia S.C., Charlotte N.C. both are a long drive the first day stopping around 9 pm but that's with a 6 am start. We had kids with us 6 and 9 yrs, so lots of bathroom/pent up energy breaks. Both get you to Disney around 5 pm with a 7:30 start next morning. Once we drove to Orangeburg which just off Highway 26 in South Carolina. I found that first day drive to be very hard. But we arrived at Disney early afternoon.
On the way back, we try to make it to Beckley, WV. That's a long drive too, but gets you back to the border in early afternoon.
Depends on whether you are used to driving a long time, and fatigue setting in when you are on a long stretch of road, you could make Orangeburg earlier than we did. I should say we don't stop for dinner until we are stopping for the night.
We didn't want to take half the week getting there as we have limited vacation time and we like to stay a full week at Disney, then chill out at a beach for a few days.
If you take 77/79 there are a lot of rest areas with picnic grounds and nice clean facilities, so bring a cooler with sandwiches and eat at those. You don't have to wait in a restaurant to get served, pay the bill etc. We really only leave the interstate for gas. Try to stay at a hotel that has a free breakfast. Once you hit I95 there aren't as many rest facilities and we would stop for a fast food lunch somewhere in Georgia.
Don't forget to stop at the Florida Welcome Centre for your free sample of Florida Orange Juice (or grapefruit)