Driving Thurs from Ft Myers to WDW, best time?

[cressy]

We'll be driving to Disney World from Ft. Myers on Thursday on our way back home to VA. I noticed tonight around 6 PM the traffic looked pretty heavy on I75, which is when we were thinking of leaving(we're spending Thursday and Friday night in WDW, leaving Saturday night). What's the best time to go to avoid the heaviest traffic? Is there an alternate route to be considered?
Thanks for any tips and/or experience.