Purely anecdotal but I accidentally fell into this during university when studying for final exams. 3 hours sleep at night, 3 hours in early afternoon. Was great and never felt better so tried to keep it after exams but it was just impossible. Once I got back to real life, it was impossible to keep such a rigid and inflexible system. I didn’t do it long enough to see any long term effects but just found it impossible to keep anyway so naturally reverted back to 7-8 hours overnight