I think it's perfectly ok to be angry that the session ends but the session has its beginning and end and the fact that it ends on time has actually nothing to do with T's anxiety. It's just the arrangement of things. If the session would be longer, it would still have to end and you might not believe it, but it could be as painful as it feels to you now.

My T has actually the same arrangement - sessions run back-to-back and the session starts exactly on time and ends exactly on time. I've been angry about it, I've ranted about it. I've accused him for not giving me enough time necessary for me to open up.

But the main problem is still that for some reason I'm not able to make use of the time I'm given the way I would like to and that's why the session time seems to short.

For some reason I allow myself excited with emotional stuff just right before the end of the session, so that I have to leave frustrated (and probably secretly hope that he became frustrated and anxious about me too).

It's not (at least for me) really about the time or the setting. It's more about what am I trying to communicate unconsciously that has to be communicated this way right in the end of the session that cannot be communicated by words while there is still time to process it.