A Round in GearHead is equal to 60 seconds.
When I started programming GH I found it convenient to have a standard unit of time, which I referred to in the docs as a round. One round is sixty ticks of the game clock; each tick now corresponds to one second. So, a speed 5 weapon takes 12 seconds to recharge. Initially I wanted one tick to represent a tenth of a second, but this granularity was too fine and caused the game to run too slowly.