My first therapist was super punctual, always starting and ending right on time. The second one was sometimes a couple minutes late starting but routinely went ~10 mins over the officially 45 minute sessions.

If it's bothersome, I would discuss time management and its meaning with the T. I did with the one who was not so strict about it and it was interesting. He said that he gauged it individually, some clients struggle to even fill the 45 mins and he tends to give extra to people like me who are very talkative in session and obviously enjoy the interaction. He even used the term "special treatment" for it, which I did not like because I don't want to be special to a therapist and don't like discrimination in a professional context. Yet I always took the extra time he offered as I did enjoy it. I also told him that quite likely if he gives extra time occasionally, but not other times, some people that are sensitive to this might interpret his withdrawing the extra negatively.

My first, very punctual, T told me once without my asking that he thought professionals who often go over the time with clients (we were talking about how I handle my students) may give out mixed signals that some people people interpret as a sign of more than professional interest. I don't feel that way about it but can imagine it's true for some.

I think if a T was very erratic about time management, I would definitely comment on it and would do it myself. I would also be bothered if my T often started me late because of another client before me, or because he needed time between clients. Or, if I knew that another client was waiting outside and the T gave me more time and took from theirs.