Full Idea
Time is clearly divisible (into past, present and future), but it can't be, because a divisible thing is measured by some part of itself (divisions of length), but the two parts must coincide to make the measurement (e.g. present must coincide with past).
Gist of Idea
How can time be divisible if we can't compare one length of time with another?
Source
Sextus Empiricus (Outlines of Pyrrhonism [c.180], III.143)
Book Reference
Sextus Empiricus: 'Outlines of Pyrrhonism', ed/tr. Bury,R.G. [Prometheus 1990], p.236