Is a bull nocturnal or diurnal?

I own two bullfrogs, and know this to be true, as they rarely go out of their hiding during daytime, and even if they do, they tend to stay in shaded and vaguely hid spots, such as in the water reeds in my tank. My smaller frog, Bumpy [They're both Juveniles, by the way.] never comes out of hiding during daytime if I am even in the room. She's a completely nocturnal hunter, forcing me to feed them during nighttime as previously mentioned.