1. The original series "24":
* The original series "24" ran for 8 seasons, ending on May 24, 2010.
2. The "24" franchise:
* The "24" franchise continued with "24: Legacy" (2017) which focused on a new character and lasted for one season.
* Additionally, there was a film "24: Redemption" (2008) which occurred between seasons 5 and 6.
So, depending on what you're asking, the answer is either May 24, 2010 (original series) or 2017 (including "Legacy").