Matsya Purana — Measures of Time: Caturyuga Computation
त्रेतासृष्टं प्रवक्ष्यामि द्वापरं कलिमेव च युगपत्समवेतौ द्वौ द्विधा वक्तुं न शक्यते //
tretāsṛṣṭaṃ pravakṣyāmi dvāparaṃ kalimeva ca yugapatsamavetau dvau dvidhā vaktuṃ na śakyate //
I shall describe what pertains to the Tretā age, and also the Dvāpara and the Kali. Yet two ages that have come together at the same time cannot be explained separately as though divided into two.
Rather than Pralaya, this verse focuses on yuga-theory: it notes that at transitions, two yugas can overlap, making their features hard to separate cleanly.
It implies dharma must be applied with awareness of the time: when yuga-characteristics mix, rulers and householders should judge conduct and policy by the prevailing blended conditions, not by an idealized, single-yuga standard.
No direct Vāstu or ritual rule is stated; indirectly, it cautions that ritual/observance standards may vary by yuga and can appear mixed during transitional periods.