WHat is the custom challenge "turn in" option?

Title says it all really, what is the “turn in” option? I can’t seem to click it, and there is no information about it.

When you complete a Custom CHallenge, you can ‘turn it in’ and then you can make more challenges instead of waiting for the current ones to do it themselves.

However, the cR will not be rewarded until the challenge time runs out, for example if I set a 3 hour challenge and turned it in with an hour to go, I wouldn’t get the cR for another hour.

It’s for those who burn through the custom challenge quick.