Is there any way to make a pet get hungry faster? Oyatsu's been full for the last 4 hours and I have food just building up in my inventory that he needs to start eating soon.

using the Malerias Clawed Glove in battle will cause random pets of yours to starve (in addition to other effects). Other than that, only time will do it. Me, I shoved foods I meant for my pets to eat into a dedicated shop.

Four hours is a loooong time for a pet to stay full, though. My own eaterpet is down to level 1 so if there's a glitch it's not happening to me.