There is a spot on 75 south of Knoxville where it drops to 1 lane, it was backed up 2 weeks ago. Find your way to US 11 if you see the backup. It only added about 15 minutes to the drive.
Grrr. I don't know what it is about Knoxville, but they just can't seem to get their road work done and left alone for any period of time. This is bad news to me. It was finally all nice and clear last October, and now they start more work there. Well, I'm glad to hear it wasn't a complete parking lot, and thanks for the notice about this. Seriously, other places always get their road work done in a more timely way, even within the state of Tennessee.
To the OP, I really think if you leave central IN by 6:30 PM, you'll be well south of Chattanooga by 2:00 AM, if you're able to keep decent speed and the stops to a minimum. Even Google Maps (which assumes driving the speed limit or less), shows under 7 hours between Indy and Chattanooga. But if you'd like to have a relaxing drive where you make a couple of stops for fun, Chattanooga might be a good bet to stop for the night. If you're willing to push it more, Marietta, GA has plenty of places to stay, and it's a little further down, but before Atlanta. Whatever you do, don't try to book a room while on the road. Have it booked well in advance, and you probably want to call the hotel and remind them you'll be checking in very late or after midnight. For example, I leave from southern Kentucky after school on Friday, and we already have a hotel booked in Valdosta, GA at Exit 18. Unless we hit a road disaster, we'll roll in to the hotel at about 11:45 that night. Then it's a 3.5 hour drive from there to WDW on Saturday AM.
Since you're going through Atlanta on a Saturday, rush hour shouldn't be a concern. Again, just stay on I-75. It's kind of fun to drive through there, I find, and see the skyline, Turner Field, etc. I drive around the speed limit through there, and am usually being passed by much faster drivers.
Kentucky is about 180 miles from Florence (where you'd get on I-75) to the Tennessee border, and Tennessee is about 166 miles (travelling on I-75) from north to south, if that helps with your timing of things. You'll spend as much or more time in the state of Georgia alone as you do in both Kentucky and Tennessee.