Poincaré's work habits

[...] his way of working further dismantles the idea that Poincaré pursued a path of pure intuition. He worked regularly from 10 till 12 in the morning and from 5 till 7 in the late afternoon. He found that working longer seldom achieved anything, but that it was not always possible to switch off, which was why he never worked in the evenings. He took a complete rest when on holiday.

Henri Poincaré
A Scientific Biography
JEREMY GRAY