American Football NCAA Rule 3-3-10-b

b. When the helmet coming off is the only reason for stopping the clock, other than due to an injury to the player or their teammate (Rule 3-3-6),
the following conditions apply (A.R. 3-3-10-I-III):
1. The play clock will be set at 25 seconds if the player is on offense and at 40 seconds if the player is on defense except after a charged team
timeout or when the game is stopped for the Two-Minute Timeout. Before the Two-Minute Timeout in the 2nd or 4th quarters, the game clock will start on the referee’s signal.
2. Ten-Second Runoff. Anytime after the Two-Minute Timeout in the 2nd or 4th quarters, the opponent has the option of a 10-second runoff, unless the helmet comes off as the direct result of a foul by the opponent.
3. If there is a 10-second runoff the game clock will start on the referee’s signal. If there is no 10-second runoff the game clock will start on the snap.
4. The 10-second runoff may be avoided by the use of a charged team timeout, if available.
5. There is no option for a 10-second runoff if helmets come off opposing players.