Nobody can truly tell you this...especially the way last season went when everyone assumed he'd only be out of the lineup for 7-10 days...not so as it turned out.
All signs point to him being cleared for contact soon. We know he won't play on PIT's opening road trip and won't be cleared for contact until after that [as he's traveling with the team and won't see any of his doctor's until he returns to PIT].
With this in mind the best case scenario has him cleared for contact about 1 week into the season. I would expect a minimum of 1 week [maybe 2 weeks given how cautious the organization has been with his injury] of taking contact and not experiencing any symptoms for him to get clearance to play.
Best case scenario [by which I mean my best and happiest guess] has him back in the lineup during the last week of October.
What I shouldn't need to tell you is how off I could be if he suffers any kind of a setback...we could be talking months.