Making the 12 hour a 10 without cheating

The 12 hour race will be ran as a 10 hour event from 8:00 am to 6:00 pm. Along with that change will be to run the 6 hour from 11:00 am to 5:00pm. then the 3 hour event will be run from 1:00 pm to 4:00 pm. I just checked and sunset is at 6:23 that day. I don't want to force that many riders to have lights for that long.