Emb,
You didn't say which city you were going to. I went to DEN for the 12 day course. Only difference between the two is that we went over everything that the CD does.
Entire program is learning about what each switch in the cockpit does. Learn the cockpit layout, and how systems are organized. Don't worry about any systems diagrams, or try to memorize where the air molecule goes in the pneumatics system. Learn what happens when you flip each switch. Also, learning the FTI preflight checklists early was very helpful for the follow on sim rides. Also helped me to understand the pre-flight checks on each system (i.e. what switches to flip for your checks).
Oral was very relaxed, and focused exactly on the above. You still get one day of review to ask any questions of instructors.
Hope this helps.