Matsya Purana — Measures of Time: Caturyuga Computation
अशीतिश्चैव वर्षाणि मासाश्चैवाधिकास्तु षट् मन्वन्तरस्य संख्यैषा मानुषेण प्रकीर्तिता //
aśītiścaiva varṣāṇi māsāścaivādhikāstu ṣaṭ manvantarasya saṃkhyaiṣā mānuṣeṇa prakīrtitā //
Eighty years indeed, with six additional months besides—this is declared to be the measure of a Manvantara when stated in human reckoning.
It does not describe Pralaya directly; it provides a technical time-measurement framework (Manvantara count) that is used in Purāṇic cosmology to situate cycles of creation and dissolution.
Indirectly: by grounding dharma and historical narratives within a structured cosmic timetable, it supports the Purāṇic view that righteous conduct (rāja-dharma and gṛhastha-dharma) aligns with larger cyclical order rather than random time.
No direct Vāstu or ritual procedure is stated; the verse is primarily chronological, offering a unit of time-reckoning that can contextualize long-duration rites, dynastic timelines, or temple-chronology claims in Purāṇic literature.