The rate at which the contacts may be cycled for reliable operation is known as the operating speed. It is limited by the actuation and release times. Actuation time is when power is applied to the coil until the contacts have settled. Release time is the opposite of actuation time. It is measured from the time power is removed from the coil until the contacts have settled again (including bounce).
An operating frequency, or repetition rate, lower than that allowed by the switching times is often specified for a relay. This is done to limit temperature rise and allow for contact settling. Of these two, temperature rise is more critical. When a relay is used near its power or voltage rating, the duty cycle must be adjusted to allow for cooling time. A lower operating frequency or altered duty cycle accomplishes cooler temperatures.