How many hours does it take to drive from Jacksonville Florida to Silver Spring Maryland on I-95?

about 11 hours
At roughly 725 miles, with three fuel top-offs (roughly 20-30 minutes each), your looking at 10 1/2 hours actual drive time, plus an hour and a half, so 12 hours total--that is, traffic permitting. There are a few pinch points along the way, surrounding larger cities, where traffic slowdowns may add another 1-8 hours. I'd estimate no less than 15-16 hours.