In the 12th letter of his Correspondence, Spinoza exposes his singular conception of the infinite in actu. In this context, he develops certain aspects of his immanentist ontology, as well as the meaning that the concepts of Eternity, Duration and Time have to him. This text then becomes central to any scholar of the question of temporality in Spinoza. There, our author distances himself from the Cartesian perspective that, on the same issue, he had exposed -not without criticism- in the Principles of Cartesian philosophy and in the Metaphysical Thoughts, both published in 1663. It is the aim of this article to study the distinction of duration and time, to underline that proper Spinozist perspective and thus show the meaning that for...