I have bad experience with these pyramid games with a preset start time. It's just comes down to a reaction time contest. I once sent within 30 seconds of the start of another game, but still didn't get paid.
Also how will you know that the time has started? If someone sends 20 seconds before 8 o clock because of their watch being wrong, will they be accepted?
to confirm the start time, I will post that the contest is open some time between 8pm and 9pm. I also will not refund any early payments made within an hour of the time I start it. This should eliminate any close calls/guessing when it will begin.
This is one of the advantages of a predetermined start time, we can work out things like this
