They are manifested or fine, being of the nature of the Gunas.
In plain words: Past, present and future are just the three Gunas showing up in different ways. The Gunas are the three basic forces of nature: Sattva (calm brightness), Rajas (activity) and Tamas (heaviness). Some things are visible, and some are still hidden.
The Gunas are the three substances, Sattva, Rajas, and Tamas, whose gross state is the sensible universe. Past and future arise from the different modes of manifestation of these Gunas.
Namaste.
A calm guide to life, the mind and the old teachings.