FWIW I've had the opposite experience. Whenever I work late the output is absolute garbage. If I work past midnight it takes me 3 hours to get done what would have taken me 30 mins in the morning, and with way less frustration and stress. Your inputs to the LLM are only as good as how fresh your mind is so I've made it a rule to not work past midnight (unless there's an emergency).

In the good old days you would reach flow and actually know when you're too tired to continue. Now you can just say "please just fix it" over and over again and get yourself in a slophole much easier.