Day 4: 12:00 A.M.-1:00 A.M. - S4-E18
Continuity mistake: To get crucial information from Prado, Jack offers his resignation to Buchanan, and takes Prado on as a private citizen. But Jack doesn't work for CTU; he works for DOD, and is at CTU on a provisional basis.
Answer: This is unintentional and a simple continuity mistake.
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