From the rulebook:

The Silver State Classic Challenge, Inc will be providing Timing & Scoring for you at the events.

EQUIPMENT

The equipment consists of 4 Arbiter GPS Receiver/Clocks tied to 4 computers to supply extremely accurate Time-of-Day from the U.S. GPS Satellite Network. A 5th computer is used to provide totally independent, manually generated, average speeds as a back up to the double redundant electronic system. A GPS synchronized atomic clock with large LED numbers will be on display at the starting line to signal the start of the event for each participant. Infra-red beams will record car passage at the Finish Line on two additional independently operating computers. The GPS Time-of-Day is automatically updated from the GPS Receiver/Clocks each time a car starts or passes through the infra- red beam.

SYSTEM OPERATION

As each car is in position, ready to start, the atomic clock will display the accurate GPS time. You will be signaled to start your time at the top or bottom of the next minute. When the clock reaches this time, this is your start time to be recorded by the computer. YOUR ELAPSED TIME HAS BEGUN! At the Finish Line, the GPS Time-of-Day will be recorded by the breaking of the infra-red beam. The precise location of the infra-red emitters will be clearly marked with large red traffic cones at the Finish Line Banner, Mile Marker 7, in Lincoln County. The start and finish times will be automatically computed to provide the elapsed time, average speed, and variance for each participant.

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Does this mean I should be able to tap into their time via GPS signal?

The distance error can be addressed with a manual reset a few miles out on the last straight. I can use any existing landmarks, but I believe adding your own is frowned upon.