Santee is at Exit 98.
This gives you 98 miles to GA, it's about 111 miles thru GA. From the FL border to I4 is 120 miles. From I4 in Daytona to WDW is 65 miles.
Now how long is determined by how fast you drive and how many and how long your stops are (and traffic conditions).
So it's 294 miles from Santee to WDW Lets round that up to 300. If you can average 60mph it's 5 hours. If there are no delays along the way a "safe" estimate is 5.5 to 6 hours. Now most people don't average 60mph, most average 50mph so it's 6 hours by the formula and most likely 6.5 to 7 hours actually.
It normally takes me about 8 hours from SOB to Deltona and that's about 100 miles north of Santee and Deltona is about 45 miles north of WDW (It normally takes me 50 to 60 minutes to get to work at the TTC)
So I don't see why it can't be realisticly done in 7 hours.