It really depends on who they are and their style as to what they ask.

Most importantly tell the truth. It's really hard for them to help if you lie to them. Also if there's something you think they should let them know. You can either mention it when they ask a question pertaining to something similar as to what you are thinking about, or mention it at the end, often times they will ask if there's anything you would like to ask them or tell them at the end of the session.

As to time I would've thought that they would have already told you. In my experience I would guess it would be around an hour or two... that would be my guess though. I've had a first session that lasted two hours, and I've had a first session that lasted 30 min, but most I've had lasted around an hour.

Good luck... and I'm sure you'll do just fine, just try not to stress about it.