Dr. A. Fruchtenbaum writes:
1 Corinthians 15:52 describes a change before bodies can enter Heaven. In verse 52a, the emphasis is on the quickness and rapidity of that change. It will be done in a moment. The Greek term translated moment is the word from which the English word “atom” comes. It is going to be in the “atom” of time.
Furthermore, it will also be as fast as the twinkling of an eye. This is not the blinking of the eye, but a reference to a sudden flash of recognition. It is like seeing a person one knows but does not immediately recognize. Then suddenly, that quick flash of recognition is what is meant by the twinkling of an eye. This verse emphasizes the quickness of the change.