1) was my first thought since it was such a small time difference, but at C speeds the physical distance they would have to be off by is something like 20 meter

1) was my first thought since it was such a small time difference, but at C speeds the physical distance they would have to be off by is something like 20 meters. Off the shelf GPS units you can get for your car are accurate to around 3 meters, and the high end models are accurate to under 30 centimeters. It would have taken a major screw up for them to be off by 20 meters.