I hear that the time inconsistency is annoying. I agree that T should take the same attitude regardless of whether it's your want to go over or hers.

Time boundaries are very important though. Even if a T hasn't got clients back to back, and I think that's not healthy or usual practise, the T should still start and finish on time. They need the ten/fifteen minute gap to process hat last client and focus on the next, have a drink, wee etc...
Also, some clients have not been able to put their own boundaries in place IRL, to say I need some time now, or thanks but I am going now...it's helpful for a T and other healthcarers to model that. Time boundaries also create a safe, predictable structure to the sessions and that can help a client feel safe and empowered.