Matsya Purana — Measures of Time: Caturyuga Computation
त्रेतायुगस्वभावेन संध्यापादेन वर्तते संध्यापादः स्वभावाच्च यो ऽंशः पादेन तिष्ठति //
tretāyugasvabhāvena saṃdhyāpādena vartate saṃdhyāpādaḥ svabhāvācca yo 'ṃśaḥ pādena tiṣṭhati //
By the inherent character of the Tretā Yuga, the age proceeds with a “twilight-quarter” (saṃdhyā-pāda). And that twilight-quarter, by its very nature, is the portion that stands as one quarter of the whole.
It does not describe Pralaya directly; it clarifies Puranic time-measurement by stating that Tretā-yuga includes a defined transitional ‘twilight-quarter’ (saṃdhyā-pāda), a key idea used in larger cosmic-cycle calculations.
By marking Tretā-yuga as a phase with a specific transitional quarter, it implies that dharma and social duties are time-conditioned; kings and householders are expected to align conduct and governance with the yuga’s prevailing moral-spiritual capacity.
No direct Vāstu or temple rule is stated; the practical takeaway is calendrical—ritual timing and tradition often rely on Puranic time-structures (yuga and saṃdhyā divisions) when framing long-cycle religious narratives and norms.