Set up time (ton): The time from power on to 90% of rated output voltage, or from AC powered on to operation of S.P.S.
Rise time (tr): The time it takes for output voltage to rise from 10% to 90% of rated value. It is usually within 50ms. Longer period than that might lead to malfunction of system.
Hold up time (th): The time from power off to 90% of rated output voltage. The general requirement is at least 16ms to allow sufficient time for UPS to take over.