Well to make it clearer on how we want to spend our time, here is what we planed to do:
Spend a full day in panama city beach: Apparently we can ride wave runner next to dolphins
A full day might be required in order to visit the Grand Canyon site
We might stay 2 night at Las Vegas (because, it think we'll need to rest a little ^^)
And we want to go to Six Flags near to LA

I've been in Key West once and I think that spending a full day there would be really enjoyable.
But regarding that I think we'll be running out of time if we start from there (instead of Jacksonville), don't you think?