I think the start/end times are to help "contain"/frame the therapy and need to be consistent. I use to get frantic getting to my T and would always be way early :-) but occasionally would be afraid I'd be late. One day only about 6 years into therapy :-) I called to tell her I might be late! (instead of just showing up late) and that there was traffic, etc. and it felt so good!!! There was a connection made between us, she didn't have to "worry"/wonder whether I was coming or not or what had happened to me (since I never missed or cancelled sessions) and so it was a "nice" thing (for her) and the connection made me feel like I didn't have to be so frantic about getting there anymore; after all, it would only be 5-10 minutes of a 100 minute session and there'd be more sessions in the week to come, etc. But it was a real breakthrough and I never got "worried" about being late again.