Day 6: 7:00 AM - 8:00 AM - S6-E2
Other mistake: At 7:45 Ahmed leads Scott out of his house at gunpoint so he can go to Scott's house. At 8:14 they arrive. But Scott's house is just across the street so we're supposed to believe that it takes half an hour to cross the street.
Answer: According to Jack in season 5, Nina was "deep cover" before the pair ever met, so it's safe to assume she was recruited before she joined CTU. As for what her primary mission was, who knows? Perhaps it was to gather sensitive intel and pass it on to her superiors. Given that she worked for an intelligence agency, it's not a stretch. Or perhaps we may find out in season seven.
Cubs Fan ★