10:00pm-11:00pm

10:00pm-11:00pm (or 22:00-23:00 in 24-hour time) is the twenty-third hour after midnight in a solar day.

Background information and notes
Coincidentally, regardless of where it falls in a particular season, this hour often features a major plot twist, turning point, or transition between the larger arcs of that season:
 * Day 1: Nina Myers is revealed as a mole inside CTU
 * Day 2: Second Wave's nuclear bomb is detonated in the Mojave Desert; George Mason is killed
 * Day 4: Air Force One is shot down; Charles Logan is introduced
 * Day 5: President Charles Logan is revealed as the mastermind behind the Sentox conspiracy
 * Day 6: Abu Fayed is eliminated; Audrey Raines is revealed to be alive
 * Day 7: Jack Bauer is exposed to the prion variant, which is played out for the rest of the season