Full Idea
There can't be a time when there was no time, so time is not limited; but unlimited time means past and present are non-existent (so time is limited to the present), or they exist (which means they are present). Time does not exist.
Gist of Idea
Time must be unlimited, but past and present can't be non-existent, and can't be now, so time does not exist
Source
Sextus Empiricus (Outlines of Pyrrhonism [c.180], III.142)
Book Reference
Sextus Empiricus: 'Outlines of Pyrrhonism', ed/tr. Bury,R.G. [Prometheus 1990], p.236