Seems to correspond to what is said in "A Mathematician's Apology" by G. H. Hardy: "Then, from about nine to one, unless he was giving a lecture, he worked at

Seems to correspond to what is said in "A Mathematician's Apology" by G. H. Hardy: "Then, from about nine to one, unless he was giving a lecture, he worked at his own mathematics. Four hours creative work a day is about the limit for a mathematician, he used to say."