The measure of a being in motion according to the “before” and “after” involved in this motion.  As such, the measurement of time presupposes a mind that can consider a motion as a single unit and thereby number it according to before and after.  However, insofar as time is founded on the motion that is numbered, one can say that time exists in reality.  According to this classical understanding of time, one avoids both the subjectivism of someone like Immanuel Kant or the absolutization of time as a kind of created matrix, as one finds in most accounts of classical mechanics.  Time is one analogate of the broader set of durations, which also includes aeviternity and eternity.