Fat can’t be broken down to create muscle. Muscle comes from proteins, which are made up of amino acids. Fat is made up of hydrocarbons. These are not the same. Your body will break down fat as energy IF there are no available macros in your digestive tract to break down, but it only uses the fat as (emergency) energy. A caloric surplus is absolutely necessary to build protein even if you are only eating protein since your body will use protein as energy (not building blocks for muscle) if it
Our bodies aren't as "locked into routine" as our brains. We tend to this so much on day-to-day and week-to-week. But we get hungry throughout the day, even if over the whole day we're in a surplus. Our metabolism is a constant thing. It doesn't reset at midnight. The idea that a present tense caloric surplus is needed for muscle growth is just not the case