Matsya Purana — Solar–Lunar Motions
दश पञ्च मुहूर्ताह्नो मुहूर्तास् त्रय एव च दशपञ्चमुहूर्तं वै अहस्तु विषुवे स्मृतम् //
daśa pañca muhūrtāhno muhūrtās traya eva ca daśapañcamuhūrtaṃ vai ahastu viṣuve smṛtam //
Daytime (āhna) consists of fifteen muhūrtas, and the night consists of three muhūrtas; thus, on viṣuva (the equinox) the day is traditionally reckoned as fifteen muhūrtas.
This verse is not about pralaya; it belongs to the Matsya Purana’s technical time-reckoning (kāla-vibhāga), defining muhūrta-based measures used to regulate ritual and calendrical calculations.
By defining muhūrta measures (especially around viṣuva), it supports dharmic scheduling—selecting proper times for yajña, vrata, royal proclamations, and household saṃskāras according to Purāṇic standards of auspicious timing.
Ritual significance is primary: muhūrta divisions are foundational for fixing auspicious moments (muhūrta) for consecrations and ceremonies; such timing frameworks are also used when choosing temple-building and installation times in allied Vāstu-ritual practice.