American Football NCAA Rule 3-2-4-b
b. 40-Second Clock.
1. When an official signals that the ball is dead, the play clock shall begin a 40-second count.
2. If the 40-second clock does not start or the count is interrupted for reasons beyond the control of the officials or the play-clock operator (e.g., clock malfunction), the referee shall stop the game clock and signal (both palms open in an over-the-head pumping motion) that the play clock should be reset at 40 seconds and started immediately.
3. In the event that the 40-second play clock is running and reads 25 before the ball is ready to be snapped, the referee shall declare a timeout and signal that the play clock be set at 25 seconds. When play is to be resumed, the referee will give the ready-for-play signal [S1] and the play clock shall begin the 25-second count. The game clock will
start on the snap unless it had been running when the referee declared a timeout; in that case, it will start on the referee’s signal (Rule 3-3-2- f). (A. R. 3-2-4-I and II)