For a 6:00 AM flight, you should generally aim to arrive at the airport between 4:00 AM and 4:30 AM. While the "two-hour rule" is standard, the early morning hours can be deceptively busy because the 6:00 AM window is often the first wave of departures for the day, leading to sudden spikes in security and check-in lines. If you are checking a bag, you must be mindful of the 45-minute or 60-minute cutoff times; arriving at 4:00 AM ensures you have a buffer for the bag drop line. If you have TSA PreCheck and are not checking a bag, you can likely push your arrival to 4:45 AM, but no later. It is also important to check when the airport's security checkpoints and airline counters actually open; arriving at 3:00 AM for a 6:00 AM flight is often unnecessary, as many staff do not begin their shifts until 4:00 AM or 4:30 AM.