It's not going towards Mars. It's going to a sun-centric orbit that gets out as far as Mars' orbit, but doesn't intersect with it. More of a "see, we can get it this far" rather than actually getting it to a specific place. Which is sensible, because a)Anything that might land/crash on Mars has to be rigorously disinfected before flight to avoid contamination of Mars with Earthly microbes* and b)If it's in a stable, non-crashing orbit, someone can go and collect it again, some far day in the future :)
All of which is to say that it doesn't matter when they launch.
*This issue is going to have to be dealt with before any serious Mars exploration.colonisation plans are put into effect