It doesn't take 12 hours to get from Columbia, SC to WDW, unless you are going a different way than we do, it takes about 8-9 hours. It takes us 14-15 hours from home in Ohio, and we go through Columbia about 6 hours after we leave home. This is from my trip notes from our trip last summer (don't laugh, I need to know where I am when traveling!). We were going to Coronado Springs and we used 417 to avoid the busiest parts of I-4.
Columbia to I-95 approx 1 hr 54 miles
(I-95 to SC/GA line approx. 86 miles)
Walterboro, SC (not too far after I-26) to Savannah 1 hr 3 min 69 miles
Savannah to Brunswick 1 hr, 13 min 79 miles
Brunswick to St. Mary’s 44 min / 45 miles
St. Mary’s to Jacksonville 36 min 38 miles
Jacksonville to Daytona 1 hr, 26 min 95 miles
Daytona to WDW about 1 hr, 45 min 92 miles
I-4 to FL-417 S to W Osceola Pkwy. Take exit 3 from 417S/W Osceola, take this to Avenida Del Centro