Dr appoinment sucks

I have a dr's appointment today and was told to not eat for eight hours. I want to know if i really cant eat for eight hours or if i could eat like six hours before? They are going to do blood work. Also I have a fast metabolism, so basically starving from ten in the evening till 10 am thats when my appointment.I understand when we are told something by a medical professionl, there is usually a reason for it. Just sucks today for me primary care dr then dentist after thats all.