I thought it looked like TT wanted to go to the corner with the pass first - then changed his mind when he saw Clay come open. If he had anticipated Clay coming open, the throw would have been earlier and probably an easy touchdown. I am thinking Clay was not the primary target there. Could be wrong of course.
Next time they run that play in the red zone - hopefully he looks at the corner route again just to look off the DB and gets a wide open Clay to throw to (sooner).