What is the turn-on time between the voltage applied to the photo diode and turn-on of the opto-coupler?
The delay time between the LED current and reaction time of the photo diode is listed as 2µs in the data sheet. It is defined as Ton and Toff.
Of more concern is the capacitive load. The output current supplied by the photo-diode is dependent on the LED current, and the gain of the opto-coupler (refer to data sheet). The opto-coupler acts like a current source. The switching time will depend on how long it takes the current output from the opto-coupler to charge the load capacitance.