Real time is such that two moments of it never coexist. In model time the moments coexists as different objects in some space. Thus Bergson calls model time a projection of real time on space. Bergson's real time is irrreversible. The seemingly inconceivable feature of Feynman's diagrams, the movement in the direction opposite to time, is explained simply by the fact that the time of physical theories is model time, i.e. a spacial phenomenon.
Real time shows up in probability theory and statistical physics.
We are dealing there with real acts of choosing from a number of possibilities. Hence this time is irreversible. In mechanics, to every action there is an inverse action which brings back the original state. So, when we project time on space the projection has an additional property of reversibility. But the act of choosing has no inverse.