In Deleuze Beyond Badiou, Clayton Crockett summarizes the 3 syntheses of time as: present (habit), past (memory) and future (death) [pp. 34-37].
Crockett places special emphasis on how the 3rd synthesis is reached through Kant, for whom “time is in the Self”. Kant’s distinction of the empirical self and active subjectivity splits the I, “and time is the name of this split”. For Deleuze, “it is as though the I were fractured from one end to the other: fractured by the pure and empty form of time” (DR 86).
Crockett says: “The pure and empty form of time becomes the opening to the future, the passage of death that constitutes the third synthesis of time. [p. 35].” This form also becomes the time-image in Cinema 2 [p. 26]. These ideas have overtones of Heideggerian temporality, but Deleuze plays them off of Nietzsche. “We repeat, become different, only by dying to our identity and becoming subject to Deleuze’s reformulation of the eternal return: only what becomes returns. Only what dies repeats” [p. 36].