The reason Wu Long slept so deeply that he allowed the two beauties to start in the morning when he woke up was because the technique that he used to sleep while being alert was indeed handy but not omnipotent. It allowed him to get his sleep, but there had to be a tiny bit of his consciousness that never got a rest, and thus accumulated fatigue over long periods of time. He normally did not feel it and it would not hinder him, but once he fell asleep without using the technique it started to rapidly recover, making up for all of the accumulated exhaustion at once, thus making him fall into a deeper slumber.
But since the whole place was covered in a grand formation he controlled and he placed talismans everywhere he was not worried. Not to mention that Ye Ling was also here and she was in Foundation Building Realm, so her mortal needs were a lot less than Wu Long's so she would only sleep once a week or so.
