Matsya Purana — Measures of Time: Caturyuga Computation
चत्वार्याहुः सहस्राणि वर्षाणां तत्कृतं युगम् तस्य ताव् अच्छती संध्या संध्यांशश्च तथाविधः //
catvāryāhuḥ sahasrāṇi varṣāṇāṃ tatkṛtaṃ yugam tasya tāv acchatī saṃdhyā saṃdhyāṃśaśca tathāvidhaḥ //
They say that the Kṛta Yuga consists of four thousand years; and that its twilight junction (sandhyā) is of the same measure, and its twilight portion (sandhyāṃśa) is likewise of that very kind.
It does not directly describe Pralaya; it lays out the cosmic time-measure (yuga reckoning) that frames larger cycles in which creation, maintenance, and dissolution are narrated.
By defining Kṛta Yuga as the benchmark age, it implicitly supports the Matsya Purana’s ethical theme that dharma varies by yuga; kings and householders are expected to align conduct and governance with the prevailing yuga-conditions.
No Vāstu or ritual procedure is specified here; its practical significance is calendrical—ritual and dharma discussions elsewhere may rely on such yuga and sandhyā calculations for contextual authority.