You can calculate the duty cycle of your actuator in the following manner:
Duty cycle (%) = (actuator on-time) / (on-time + off-time)
So, if your actuator operates for 15 s. and then rests for 45 s. during a 1 min. cycle, your duty cycle is:
Duty cycle = (15 s.) / (15 s. + 45 s.) = 15 / 60 = 0.25 or 25%
Duty cycle ratings vary. Be sure to check the product specifications. Some duty cycle ratings change based on the loading on the actuator. This is especially true for DC actuators. When loading is a factor in duty cycle a chart will be included in the product specifications to reference.
There are also other factors that can influence an actuator's duty
cycle, such as ambient temperature, loading characteristics, the actuator condition, etc.