I think if there is enough material for 90 minutes, then go for it (if T is willing, of course). We used to schedule 90 minute sessions when we would do EMDR, as 50 minutes was too short to get through the protocol adequately. I have also had a few 2 hr sessions, especially couples. This is especially useful if you have certain things you MUST accomplish during the session (some sort of deadline you are trying to meet). My initial session with our child specialist was 4 hrs. But I was so glad to get so much out there on the table at once. It would have been really inefficient to come back 4 weeks in a row for 1 hr each time.

I will be interested to hear what your T says. Some Ts really like all the sessions to be the same length. I think the downside to a longer session is if you cover so much in the first half that you need processing time and you won't have that if you immediately go into the second half of the longer session. I know when I was doing trauma work, I often really needed processing time between sessions.