Campaign questions, trying to avoid spoilers & opinions

As I await the campaign downloading, I am reading some confusing info about progress in the campaign. I am curious of a few practical things, so I can plan how much time I need to set aside before I play for a session this weekend, but to avoid spoilers, would rather not search for them.

How long does the campaign take to complete?

How long of a session is it between saves or checkpoints that allow a break to quit and come back? (are they similar length? or some sections much longer / shorter)

How many sessions or sections to complete the campaign?

Thanks ~ ! Hope everyone has a fun weekend playing !