A fundamental dimension in macroeconomics, time, is rarely portrayed as a prominent theme, because of the sharp contrasts that have historically divided economists using alternative conceptions of time, but also because of the conundrums brought about by incorporating time into economic models. This chapter provides an interpretation of John Maynard Keynes’s methodological reflections on the concept of time as (among others) complex and manifold magnitudes, which – confounding the choice of units for macroeconomics – requires economists to carefully avoid inconsistent logical reasoning about its characteristics, and instead to focus, as Keynes did, on change and transition.