Although the final launch of Space Shuttle Endeavour is just under 9 hours away if you want to watch it from the Space Coast you should be thinking of leaving very soon.
There have been many reports of the number of visitors expected to watch the launch ranging from 500,000 to 750,000 all in the relatively small area around Kennedy Space Center. That is a heck of a lot of people in such a small area. The worst thing will be getting in and out of Brevard County.
If at all possible try and avoid the SR528. For the launch of STS-133 Discovery by 10am the SR528 was a car park. The authorities did their best to keep traffic moving by removing the tolls, but the sheer volume of traffic just clogged the freeway.
The way to avoid it is by leaving as early as possible and taking an alternate. Last time coming from the west I found the SR532 quite clear then hit a little traffic as I passed the I95. Coming from Orlando you could try the SR50 or a bit further north the SR46.