Photons travel at the speed of light. At the speed of light, time is zero. Therefore, photons don't age. Consequently, the interaction between source and destination is instantaneous. This means that a source doesn't have to "wait" for a propagating wave to reach a destination for an effect on the source to occur.
It can be seen that phenomena such as instantaneous interaction between opposite spin pairs propagating away from one another, each at the speed of light away from the point where the pair was generated, does not violate relativity. Because the particles are moving at c, time is zero, and reactions are instantaneous between the particles. There is no need to postulate hypothetical particles communicating information between the spin pairs.
In diffraction, it is assumed that virtual particles are necessary to explain the interference patterns which form due to the diffraction. It is assumed that virtual particles return back to the photon's origin to communicate the status of the photon at the interaction point. The existence of these virtual particles becomes extraneous if it is assumed that the photons at the creation point and destination are the same age, i.e., the photons travel and arrive in zero time.