I wouldn't start a rookie over an incumbent starter unless the team had an open competition (we didn't), and he earned the job outright. He's had some time with the ones due to injury, and the coaching staff has seen more of what he can do than maybe they planned. We saw some good stuff from him in the preseason.
He's already the #2 over another player that the team brought in with more experience. Now he'll get some experience in game planning, and film study prior to each match-up. He likely has a long way to go there. They can now spend some more time in practice getting him reps on what he most needs to work on, and get him ready for when he inevitably steps in.
Starting NP over TT at this juncture would alienate the team imo, and signal the thought that the season is lost before it begins. TT needs to play poorly enough to lose the job, or get injured, for it to feel like NP deserves a chance to start.