Exact timings of the JR Pass

Hello there,

I have a 12 day trip booked for Japan in March. If I were to purchase the 7 day pass, could I use on the early morning of the 5th March and then at night on the 12th March?

Does the pass only work for 168 hours (7 days)? If yes, the the pass will expire early morning on the 12th March (if I use early morning on the 5th March).

Kind Regards,