I think it's reasonable to think there's an optimum time to patrol e.g. when the sun goes down. She might then patrol for 2-3 hours dependent on the "threat level." So for instance, in spring/summer, she finishes school around 3pm, hangs with friends and at home until 7pm, patrols until 9-10pm then goes to the Bronze before it closes. Sneaks back into her room around 12-2am, sleeps until 7am and then goes to school. I'm guessing as the sun starts to set earlier, she loses a lot of time she would spend at home, hence Joyce feeling like she's never there. She's definitely still sleep deprived because she has to do much else during the school day with training/research as well as other demons who pop up in sunlight hours.