Am I entitled to more paid hours?

I am an hourly employee that works at an agency that supports people with developmental disabilities. Many of these individuals require 24 hour supervision. Occasionally, I accompany an individual on a vacation. Because the agency argues that I am getting a free vacation they need only pay me 8 hours a day. I feel I am entitled to more as the person I am with does not stop needing help at 8 hours. I am still performing job duties as described in my job description. I would be okay with not being paid while I am asleep as I am not performing job duties then. Am I correct that I should get paid for more hours?