For monochromatic light with a frequency above the threshold, all the photons that strike the plate have enough energy to release an electron. This means that as soon as photons strike the plate, photoemission occurs. There is no delay while waiting for the electron to gain enough energy because all of the photon's energy is transferred to the electron instantly. Delay would only be introduced if we performed the experiment over such a long distance that the travel time of the photon became measurable. This would require a very large distance!

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