I know what the photoelectic effect is.
It's my understanding that the electron emission can occur due to photons (which have to have the right amount of energy or more), heat, and various other sources. If we talk about the photoelectric effect due to heat, I understand that over a period of time, the heat would build up and free the electron (whereas with photons, it couldn't use 2x photons which each had less energy than the work function - each photon has to have the correct energy).
However, I've just seen a question about the photoelectric effect involving UV photons, and it said that over a period of time, more electrons would be released. Why does time matter? Why would the photons keep coming from the UV source over a period of time, and not instantly? Is it because a UV source would constantly be emitting photons?