Final answer:
The referee can correct timing errors on the play clock before the snap of the ball. Errors discovered after the snap often stand unless they significantly affect the play.
Step-by-step explanation:
A referee in a football game can correct obvious errors in timing by the play clock before the snap occurs. This allows for any mistakes made in the countdown or stoppage of the play clock to be rectified before the play begins, ensuring the game continues under the correct conditions. If the error is noticed after the snap, the play typically proceeds, and the mistake may only be addressed if it has a significant impact on the play that unfolded.