Tackles usually step up big time in year 2. Some guys that don't get it in year 2 will pick it up in year 3. But in general, tackle's not a really a late-bloomer position. Some small LTs need a couple seasons to get stronger, but usually it's the feet that make or break tackles, and you can see that immediately. They just need some live reps to adjust to a way harder NFL playbook and to the speed of the defensive mutants across from them.
Anyway, what you want to see from Guyton in year 1 is signs of life. If he's an average LT, that's a big win. Even if he kind of sucks, that's still a good sign.. A lot of rooks will start the season strong and then fade, or struggle for a couple months and finish strong. I'll take either. I just want to see some signs that he can play.
If Guyton can just hang on and survive, then I'd expect big improvement to come quickly thereafter. But if he's out there looking lost, or if he can't beat out journeyman backups for a starting gig, that will a huge problem.