I was just reading this question and I didn't understand the question at first. But I think I understood it after a bit of thought. Here is my question inspired from that question:
Are the processes of pair production and matter-antimatter annihilation instantaneous? If not, what are the intermediate forms of matter-energy involved in the process?
NOTE: I don't know exactly how weird quantum mechanics is. But is the answer that there is no sense of instantaneous at the sub-atomic level?