We ran timed sections on the BDW two years ago. We sync'd two stop watches to run at the same time. The finish marshall had 5 min start to set up and then the numbered riders started on minute intervals, the first starting at a pre-determined time. The finish marshall just had to record the times to determine the winner. It worked really easily.
For the record, the winner was Ed Orange.
For the record, the winner was Ed Orange.