Unlike the Stoics and Epicureans, most of the Platonists from the first century BCE onwards (the so-called Middle and Neo-Platonists) held that since the cause(s) of the cosmos (the ordered universe) were eternal (the paradigm-forms and the creator God/Intellect as their mediator to receptive matter), then the cosmos must also be eternal (since the eternal activity of the eternal cause is direct).  The myths and allegories used by Plato, including in the Timaeus, were understood not as literal descriptions of an ‘historic’ act by a creator/craftsman, but rather as the activity of an eternal intellect suffusing dynamic matter and bringing creative shape and order to it in accordance with the paradigmatic Ideas of his (the creator’s) mind.
With certain Platonists (or Platonist-adjacent thinkers) this was not so. For Plutarch, Philo, and Atticus for example, the ‘cosmos’ did have a beginning (although whether it had to end was up for grabs).
Plutarch (1rst and early 2nd century CE) is a philosopher I’ve grown very fond of in recent years. He was a priest of Apollo and while not a startlingly original thinker, was broad in his scope, respectful and interested in a variety of religious forms, particularly the Egyptian but also the Zoroastrian Iranian, and generally a sympathetic, cultured, liberal and affectionate man.  Philosophical  ‘innovation’ in any event was generally considered deviation in this post-Hellenistic period where at least the aura of conservativism and appeals to ancient tradition had ironically become more appealing than originality. This may have been a consequence of the expansion of the Roman empire, and hence the greater need on the part of the intelligentsia to be able to find unifying values in a plurality of hitherto foreign traditions. Cosmopolitanism required a dialling down of the effort to break new philosophical ground and a dialling up of ways to accommodate and translate venerable traditions. It might also be caught up in the tendency towards seeking transcendence and a sense of disillusionment with materialist philosophies. But Plutarch did in fact innovate quite starkly for a Platonist in respect to the question of whether the cosmos had a beginning or not. Was there a temporal creation moment which ‘began’ the cosmos? Plutarch argued that there was.
Briefly, his argument is that there should be a distinction made between two concepts of time;
a-the time relevant to the ordered universe, the cosmos as it was brought into existence by the creator (whom he identifies as Osiris, but the name really doesn’t matter; in effect it’s the same creator God/Intellect under any name),
and b- the time relevant to pre-existing ‘chaos’, which is a term for matter without shape or order.
Matter is understood to be always in motion, whether it is chaotic or ordered. Since it was also understood that time meant motion or change ( calculated), time must be unbounded and beginningless. But time specifically related to the ordered universe, as opposed to pre-ordered chaos, might not be. (Added; Plutarch would actually deny this is really time at all, just incalculable activity)
If the distinction between the two ‘times’ was the intervention of the creative intellect (God) then it could be claimed that the cosmos had a beginning. This was not a very popularly held view, certainly among Platonists, but I think it’s a very interesting argument.
From a Buddhist perspective, this Plutarchean argument for a beginning to the universe as it is normally understood- the distinction between chaos and cosmos, and between their times- could be addressed thus;
Chaos and order,
Eternal and temporal,
Matter and mind,
These are a dualities.
Dualities arise with the analytical/discursive mind.
The analytical/discursive mind is bound up with the birth and death of conditioned beings (humans)
Unconditioned reality is non-dual.
Therefore mind (even ordinary human mind) if it can recognise the conditioned nature of dualistic thinking , if it can transcend it's own immersion in dualistic thinking, can put an end to these aporetic confusions and awaken AS the ultimate reality from which it has never actually been separate.
Doubtless, and I mean this directly, any incarnate perception of time involves motion. So the question arises, are we perceiving time?
There are quite a few ways one could answer that, but it still comes down to motion, or the result of motion, which is the indicator towards the existence of what we flippantly refer to as time.
Can we then, even speak of time, as anything but an effect?