— After finishing 2 hours of his morning training with Luke, Rio has to freshen up and then get ready for breakfast with his family. After spending all his energy on that training, obviously he needed to eat a lot to fill his stomach to recharge himself. Plus the food always tasted so good that he couldn't eat less even if he wanted to.
— At 9:00am, a different type of hell starts. His theory classes, for 3 hours straight he needs to sit and listen to different people coming and going, teaching him about Arcadia's history, world affairs, dungeons and monster anatomy, basically all kinds of stuff he should just know by heart, if he wants to live well. The teachers who came to teach him were obviously very knowledgeable and experienced.
Now this may sound easy since Rio already knew some stuff before from the novel, but it's not. He had just eaten his fill and his body needed sleep. Keeping his eyes open during this period was a mental torture.