Based on their Earth->MArs trajectory, they might have to stay for possibly a terrestrial year or more, waiting for the next launch window to Earth.
Provided you want to get the crew back to Earth of course, if not then "don't need to be there more than few hours" takes a whole another meaning & makes mass optimization of the mission much easier! ;-)
We need to do some basic expreriments, take the soil samples and drill few meters down in order to check for water ice deposits.
But before all that, we need to send more rovers.