438 days. That's one year, two months and two days shy of two weeks. You have a funny way of rounding up that figure.
But while we're on the subject, perhaps you'd care to also do some fact checking on the supplies that were sent up to Mir and the crew rotation. Those alone appreciably altered the experience of the cosmonaut in question. Such alterations will not be possible in the Mars mission.
On a mission to Mars, the astronauts would only be ship bound for a period of six months.
And bound to the confines of their lander and enviro-suits upon landing. The atmosphere on Mars is carbon dioxide.
I would also presume that scientists are/will be working on a fast mode of travel so that the 3 year round-trip is sped up considerably.
The most they'll be able to shave off is perhaps four months...unless they figure out how to alter the orbit of Mars to make it synchronous with Earth.
In any event, I'd favor skipping the return trip and moving towards immediate colonization.
And once again I ask: do you have any idea how many metric tons of water, food and oxygen must be shipped in order to fulfill even the most basic needs? And what of emergencies? How do you intend to address a number of situations that can come up while that far isolated from Earth? Judging from your abundant avoidance of those stubborn facts, it's pretty apparent you either don't care to know or just don't care at all.