Full Idea
It is the circular movement of the soul that constitutes time, just as the permanence of intelligence in itself constitutes eternity.
Gist of Idea
Time is the circular movement of the soul
Source
Porphyry (Launching Points to the Realm of the Mind [c.280], 5Enn3 32(5-7))
Book Reference
Porphyry: 'Launching Points to the Realm of the Mind', ed/tr. Guthrie,Kenneth [Phanes 1988], p.50
A Reaction
Plato loved circles. If you think time is subjective, this is trying to express your intuition. Personally I think it is nonsense