At 11:59 p.m., a Silent Clock marked the death of Teri Bauer and the final minutes of the show's first season.
George Mason: At 9:35:56 p.m., a Silent Clock was displayed after Mason's final departure from CTU.
In the final hour of Day 2, when an attempted assassination took place on President David Palmer, the episode and the season ended with a Silent Clock . However, the clock ticks with Palmer gasping for breath instead of the normal ticking sound. It is disputed whether this counts as a Silent Clock.
At 6:59 a.m., Jack Bauer was forced to kill Ryan Chapelle. A Silent Clock honoured his death. The "tick tock" sound was replaced by the sound of a train in the background.
Edgar Stiles, while looking for a missing CTU agent before the terrorist's gas attack on CTU itself, was unable to get to a secure area before he succumbed to the effects of the nerve gas released in the building. As a horrified Chloe O'Brian tearfully looked on, Edgar fell, and his death at 6:59 p.m. was the fourth to be given a Silent Clock.
https://24.fandom.com/wiki/Silent_clock
