Yes, It has a stored energy in that stone.
The intensity of the light has no connection with the photoelectric effect.
That's what was so baffling about it before the particle nature of light
was suspected ... a match with a blue flame might stimulate the
photoelectric effect, but a high-power red searchlight couldn't do it.
It is c which is four minutes per day
A solar eclipse or lunar eclipse can occur at any moment of any day of the year.