Can I Join a Challenge After It Starts, or Leave One I've Joined?

Joining after a Challenge has started

In most cases you can still join a Challenge once it is already underway, it does not have to be from day one. Once you opt in, your logged activity starts counting toward that Challenge's Leaderboard from that point. Exactly how joining partway through affects your standing can vary, so if you are chasing a milestone or a placement, it is worth checking with your organiser.

Leaving a Challenge

You do not need to do anything to stop taking part; if you stop logging activity, you simply stop moving on that Leaderboard. Whether a Challenge also lets you formally opt out or remove yourself from view depends on how the organiser set it up, so check the Challenge's details screen in the App or ask the organiser if you want to be sure.