"In a vacuum, electromagnetic waves travel at the speed of light, commonly denoted c."
I would expect that in air, that the photon from the light source and the perturbance of the electric field from the charge to reach the detector at the same time.
It moves at the same speed as light (it is light), but not at the "speed of light" (c). Light/EM waves move slower than c in air (and much slower than c in a copper wire).
It's close enough to c that you should just use c but it can be observed that it's less.