A study in circadian rhythms show problems astronauts could encounter on Mars.

However, Michel Siffre (being isolated in a cave for a very long time without a watch) showed his stabilized at 25 hours.

Anyway, what is important are the 6 months of the Mars bound trip. Astronauts must be in sharp form when they land.
The trip, outside of the Van Allen Belt (hello continuous flashes in the eyes, when closed!), with nothing to see outside (Earth and Mars being too small and the Sun or its reflection on the hull being too bright), in weigthlessness (hello 2 hours of exercizes, every day!), (and if everything works properly, boredom, or if there are technical or psychological problems , stress) , is going to be such a challenge that it will have to be preceded by months long trips in orbit around the Sun, but close to Earth, and gradually get to Mars.

Raoul