Only really dumb RC would close the finishline after 20 minutes in a handicapped fleet with rating ranging from say 100 ro 129.

Sadly there are alot of dumb RC's around in the world.

Best is for the RC to note down the difference between the fastest and slowest rating of the fleet before going out on the water and use (Rating difference) + 15 minutes as the closing time. This allows all boats to have at least 15 min to get relative to winning the race.

Wouter