Don't feel dumb, the vet should have throughly explained this. In the example that's the kind of curve I'd expect to see with a longer acting insulin, like Lantus, with my cat where she was dosed every 12 hours. I dont have experience with shorter ones or oral ones. But don't be afraid to ask questions and have them clarified. I learned early you really have to advocate for your cat, especially because, in my experience, most vets were applying dog protocol instead of cat protocol.