This app is a toy for considering the nature of subjective time and the duration of the present. Some theories have it that discrete instants of time follow each other sequentially like beads on a string and that our memory of each preceding bead opens up a window of duration. Others, like the Specious Present of William James, view the awareness of time itself as durational: a window of passage that occupies anywhere from one-half second to twelve seconds (James himself considered the window of the present anywhere from about three to twelve seconds).
What you see in this app can mirror these durational windows spanning a range of variable nows. The upper camera window trails the lower, delayed by a variable number of seconds (controlled by the slider). Together these split-time windows portray, perhaps, twin selfies of the specious present.