When an atom or electron absorbs a photon, before the interaction you have an electron and a photon (possibly virtual). Afterwards, you have an excited electron (or atom). How much time does it take for the change?
According to my simple understanding,the change, when it happens, is instantaneous. It would seem that conservation of energy requires that at an exact time the photon goes away and the electron/atom goes to a higher energy state. This does not seem in the spirit of quantum mechanical variables that are usually associated with an uncertainty.
Is there in fact some delta-t for the event duration?
It seems strange that such a classical mechanics notion of a variable, time, carries over into QM.