Your post made me realize that I have rarely, if ever, encountered any definition/explanation of the concept of time in Advaita. It set me off on a search of my library to try to find something. Apart from those books which index every word they contain (e.g. Krishnaswamy Iyer’s ‘Vedanta or the Science of Reality’ has 107 page-references to ‘time’), I could not find anything in any of my physical books. A search of my electronic database came up with very few references and the only scriptural one I could find is from Vivekachudamani 497:
sthulādibhāvā mayi kalpitā bhramā-dārōpitānusphuraṇena lōkaiḥ |
kāle yathā kalpakavatsarāya-ṇartvā dayō niṣkalanirvikalpe ||497||
John Grimes translates:
Sthūlādi = gross and so on; kalpita bhramāt = erroneously imagined; āropitānu-sphuraṇena = manifestation superimposed; kale = time; kalpaka = eons; vatsarāyaṇa = years and half-years; ṛtvādi = seasons and so on.
But, whether it was an author or a publisher error, the key phrase is missed out. Time cannot actually be divided up in this way because its real nature is niṣkalanirvikalpe – niṣkala (without parts, undivided); nirvikalpa (free from change or differences).
Hari Prasad Shastri translation gives:
It is in me that physical (perceptible) and subtle (Imperceptible) beings are imagined through error. But people merely superimpose them as empty phenomena. It is as when people imagine, in time, which is partless and undifferentiated, divisions such as world-periods, years, half-years, seasons and so on.
It is similar to the confusions that people have resulting from the difference between what is real (sat) and what is mithyA (dependent reality). We talk about a ‘gold ring’ and the understanding is clearly that the ring is the reality, the noun, and ‘gold’ is merely an adjective describing it. But, of course, it is actually the complete opposite of this. The ‘gold ring’ is always only gold substance; it just happens to be temporarily in the form of a ring. ‘Gold’ is the noun and ‘ring’ is really the adjective, indicating the name and form of the gold at this moment in time.
It is the same when we come to talk about the brain and consciousness. Scientists blithely speak about a ‘conscious brain’. The brain is the noun and it currently happens to be described by the word ‘conscious’. We may say that it has ‘consciousness’, thus treating that now as a noun itself, but there is no doubt that science regards the brain as the substance, which may have consciousness. If you knock the head with a heavy object, it is very likely that the brain will cease to be conscious! Point proven so they think!
But, of course, Advaitins know better. Consciousness is the only real ‘substance’. The brain just happens to be the name of a form that may ‘reflect’ or ‘transmit’ or appear to ‘possess’ Consciousness. Knock it on the head and the reflection may cease for a while but the Consciousness does not go away! The brain ‘borrows’ its consciousness (small ‘c’) from Consciousness (capital ‘C’), in the same way that the ring ‘borrows’ its existence from gold. Just as gold is the substance, with ring merely a mithyA name and form, so Consciousness is the substance, with body and mind merely mithyA names and forms. In this way, the real and the ephemeral are interchanged.
Similarly, says the author of Vivekachudamani, we speak of periods of time as though time were something that could be broken up and sub-divided. In fact, time is changeless and part-less. What we call a ‘year’ is entirely arbitrary; it just happens to be how long it takes the earth to orbit the sun. A ‘year’ for other planets in the solar system differs widely. Similarly for the other ‘units of time’ that we devise for our convenience.
Time itself does not change. It is the changeless principle that (as if) causes change in the form of the mithyA objects of the world. Our mental division of time into seconds or millennia is analogous to our mental division of gold into bangles and rings.