I would strongly urge you to reconsider heading to Orlando at all. It's nighttime, now, so the roads are mostly quiet, but during the day, they've been complete chaos. A friend of mine left Fort Lauderdale Wednesday to head north. In 5 hours, she didn't even make it to Orlando. It's usually about 2 1/2 hours.
As of 1:00 am eastern time, Friday, I-75 is totally backed up northbound from the Florida Turnpike entrance (which is the link to WDW), all the way to Valdosta, GA. There's accidents all over the highways between Miami and Orlando. You'd be going the wrong way, so things are clear to Orlando right now, but things may change very quickly.
If an evacuation order is issued The State of Florida, the highways may all point northbound, thereby, you may not actually make it to Orlando without using surface roads, which could double or even triple the time to get there. It's also highly likely that you won't actually make it to Orlando at all.
Gas has been in very short supply in Florida as all of the residents are getting what they can and getting out. If you fill up at the Georgia State line, provided you can find gas, it will take about 1/2 a tank to get to Orlando. There's no guarantee you'll have enough gas to get back to Georgia. If you're coming from Alabama, you won't make it.
No vacation is worth your life. This hurricane has already killed people, and has practically destroyed the country of Barbuda, and has knocked out the entire power system Puerto Rico and The US Virgin Islands. PR is saying it will take 4-6 months for the power to come back. We don't know if Barbuda can recover from this.
WDW is offering full refunds of any cancellations due to Irma. Stay safe, and if you don't HAVE to be in Florida this weekend, please, don't.