@Flyerfan, My guess would be your flight had a large number of people connecting, many from airports east of Las Vegas. With check-in starting 24 hours before the first leg of an itinerary, those people get a bit of a "leg" up. Say someone in eastern time zone is connecting through Vegas. Their morning started three hours ahead of yours because of the time zone change. Then they took a 3-4 hour flight, which probably arrived an hour or two before their connection (your first flight) took off. So in that example, those passengers had a nine-hour window available to check in before your check-in opened up.
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