Matsya Purana — Yuga Durations
द्वापरं द्वे सहस्रे तु वर्षाणां रविनन्दन तस्य तावच्छती संध्या द्विगुणा युगमुच्यते //
dvāparaṃ dve sahasre tu varṣāṇāṃ ravinandana tasya tāvacchatī saṃdhyā dviguṇā yugamucyate //
O descendant of the Sun (Ravinandana), the Dvāpara Yuga lasts for two thousand years; its twilight period (sandhyā) is of the same measure in hundreds, and the yuga is said to be double when the junctions (dawn and dusk) are included.
It does not describe Pralaya directly; it defines cosmic time (yuga-length and its junction periods), which is the chronological framework used in the Purana to situate creation, decline of dharma, and eventual dissolution.
By teaching yuga-measures, it implies that dharma and social duties are applied with awareness of the age’s conditions; rulers and householders are urged in the Purana to govern and live according to the moral strength of the yuga and its gradual transitions (sandhyā).
No specific Vāstu or temple rule is stated; the practical link is that rituals (especially sandhyā-related observances) and calendrical timing in Purāṇic practice rely on accurate concepts of cosmic time and transitional periods.