Why wouldn't he just do this at the beginning of every day and act as a cultivator instead of doing it at the end and then sleeping?

I don't want to encourage other to not read this as it is a good, quality novel but there were some things that personally bothered me. I just wish the author put more thought into the background and beginning development of the character, even just a little uniqueness would have improved the quality alot. Like father left, mother in a comma, and dungeons all over the world. I get it works but try to have a little spin. The MC is also just Arifureta but with spacial abilities, white hair, loses a arm, eats monsters and gets lightning affinity is literally an exact copy. One last thing is I don't understand was how it took him 6 years to find out seemingly obvious things about his ability and how he wasn't able to get his class in this time when he had no trouble killings beast as soon as he gets stranded. Otherwise I like the development, just pointing out some flaws so any future novels are even better. :)

how does he know

Heh.