Every time you hear the starting beeps and reach down to grab the bar for the first time, or the handle on the rower, or you crouch down for your first burpee - it's time to get some work done.
It's not time to game the WOD, to analyze how much you put on the bar, how quickly you can do the reps or even how bad it is going to hurt.
It is time to work.
It is time to keep moving and get through rep after rep.
It is time to block out all of the voices, to let the music move you - to go into your dark place.
When you hear GO! it is time to stop thinking, and start working.
You can think about it before you step up to the bar; you can think about it as you are laying on the floor.
You can analyze how you did after, you can game your pace for next time, later.
For now, however, just work.