The precise duration of each journey depends on when it is taken. Because both Mars and Earth's orbits are not perfectly circular, the time it takes to travel between them varies from five to ten months. There is a window every 1.6 years when Mars is closer to Earth.

The total journey time from Earth to Mars takes between 150 - 300 days depending on the speed of the launch, the alignment of Earth and Mars, and the length of the journey the spacecraft takes to reach its target. It really just depends on how much fuel you’re willing to burn to get there. More fuel, shorter travel time.

It may not sound like a lot, but when you're stuck in a space shuttle with another person in a space suit doing many tasks over and over or just watching videos for almost a year, the extra amount of time (extra number of days) will count.

More Info: www.universetoday.com