Your shield drains over time. Stay in first to keep your shield draining at a slower rate.
No weapons, no pitlane, no afterburner, ships don't take collision damage and everybody behind the lead gets a turbo every lap.
Rush Hour was added in version 1.2 alongside the Outer Reaches Expansion. In this mode, all ships' shields drain slowly over time, with the speed of the drain decreasing the closer the ship is to first place. Like in Knockout, the race ends when only one ship is left intact.