Why does the relay trip delay time does not go below 1 cycle in Arc Flash?

Per IEEE std 1584-2002, section 4.6, p.8:

"For relay operated circuit breakers, the relay curves show only the relay operating time in the time-delay region. For relays operating in their instantaneous region, allow 16 milliseconds on 60 Hz systems for operation."

In PTW v7.0.4.8, relays with intentional Instantaneous delay will be able to report trip times below 1 cycle. If there is no set delay, it will show 1 cycle.