Option #1: Pensavo che avessimo dovuto partire verso le 8.00.
Option #2: Pensavo che dovessimo partire verso le 8.00.
So then I thought, hey, I have a handy-dandy Italian boyfriend, let's see if he makes himself useful...
Io (me): I want to say 'I thought we had to leave around 8am this morning', would I say avessimo dovuto partire or dovessimo partire?
Lui (him): Avessimo dovuto partire.
Io: So what would dovessimo partire mean?
Lui: Means I thought we had to leave.
Io: And instead, avessimo dovuto partire means?
Io: Ok well how do you pick one?
Lui: Just pick one.
And that folks, is the extent of explanation I get from my Italian teacher. Please leave your own explanation or suggestion in comments should you have a little more insight than Massi, I would appreciate it!