I'm pretty sure the v5/v5.5 drop hunger/happiness hearts every hour and poop every two hours, regardless of what stage it's in. I really do feel like this Tamagotchi needs to be run alongside another Tamagotchi.
The babies get hungrier sooner, but once they evolve it takes longer for it to go down. Usually it takes 30 minutes for my hearts to go down. I guess its good, because you dont have to feed it every minute... ^w^