I would hope sooner than later, if he is physically ready.
Not like next year this will be a Superbowl team with a Dallas 90's offensive line.
There will be some growing pains and some struggles but IMO the player either has it or not. No amount of time learning on the bench will prepare them.
Some can say the Chiefs only started Mahomes once his rookie year, but you can also argue that Reid went with the safe hand with Alex Smith(who had a good year) and they were going to be a playoff team with AS. Not like they were a rebuilding team and they started some washed up QB over their rookie QB.
Joe Burrow has looked good for a rookie on a bad team, and Herbert had a good game vs the Chiefs, and he didn;t know he was going to start till right before kickoff.
I see no reason why Tua can't be getting experience now unless he either looked bad in camp or isn't fully recovered.