Afaik, humans never tried to live according to shorter or longer days so the Martian astronauts might be the first humans from Earth that have to follow a different cycle. The Martian day (Sol) is about 40 minutes longer than the Terrestrial day. Martian astronauts might take particular clocks with them that follow the Sols instead of Earth days. Was it ever tested what effects the longer days would have on their health? Perhaps Mars' low gravity would have counter-effects since the astronauts wouldn't have so much effort in the low gravity environment. I think that astronauts in space don't sleep so long as on Earth because they don't get as exhausted in microgravity as in 1 g. So the longer day might not be much of an issue for Martian visitors if they don't get so exhausted in 0.38 g. Or would it be better to land near the Martian poles to follow the Earth's cycle while having permanent day on the Mars pole?