The film "The Martian" opens with the expedition ending early due to a dust storm - the crew evacuates to orbit and their mothership, the Hermes. The Hermes then departs for Earth, and after quite some time, Earth discovers what has happened to Watney (the Hermes crew doesn't know).
This all lays the impression that after the early evacuation, the Hermes departed for Earth immediately, moving up their departure by some weeks.
However, missions to Mars require some fairly critical ∆v calculations and timing (so the planets are in the right places) to minimize fuel burn. Wouldn't you expect Hermes to remain in Mars orbit until the planned departure time? Or did Hermes have abilities which allowed it to take disadvantageous routes?
It seems like it would affect the story if Hermes had remained for awhile...