Something like this happened to me last week. I sat in the waiting room and the client before me came out of her room about 3 minutes before my time. So T went over time, because I first had that time. Around the start of my time she came out of her room, went somewhere, I think to get something and then went back into her room. About 4 minutes after my session supposed to start, she came to get me.

I know 4 minutes isn't the same as 10 minutes late. But there's always at least 15 minutes between sessions and I know that during that time she does some paperwork on the client and maybe look at the notes on the next client.
Even though it's only 4 minutes, I was pissed. It makes me feel like I'm not important, like she doesn't really want to see me. My session stopped on time.
I didn't said anything.

And months ago it had also happened. Twice. The client before me walked out at the start of my time, and T walked out with her. And she also had to go to the bathroom. And I didn't got extra time. I was so angry, but I didn't say anything.
Those were the only times I've been angry with T.

My T sometimes had to go to the badroom, when she came out of her room at my time. But that I didn't mind, because it wasn't because she let a client stay longer. Which I know because I'm usually too early there.

O, and when I had the time after lunch, which I had for a couple of weeks before that asshole client got that time, she was about 2-3 minutes late. I think it was because they have 3 buildings where the offices are and lunch they do in another building where T's office isn't, so she had to walk from there to her office. I was a little bit annoyed by that.

Usually my sessions end on time. The only times I had some extra time, were when she didn't had a client after me. I don't get why she sometimes let clients before me go over time, yet my sessions she always end on time.