SpaceX has declared an intention to launch a "Red Dragon" spacecraft for a soft landing on Mars "as soon as 2018," per the initial announcement on twitter.
Per the more detailed article, this will be a joint effort with NASA, with NASA providing technical support in exchange for data taken by SpaceX's craft. The mission will employ SpaceX's "Falcon Heavy" for launch and a new version of the "Dragon 2" spacecraft for transit.
The biennial Mars low energy launch window is from April to May 2018.
Will SpaceX successfully launch a rocket towards Mars in this window?
This will resolve positive if SpaceX successfully launches a rocket towards Mars by June 15, 2018. "Successfully" here will mean that a spacecraft is on a Mars trajectory and in control as of time of completion of its last main engine burn to enter cruise phase.