Matsya Purana — Yuga Durations
त्रीणि वर्षसहस्राणि त्रेतायुगमिहोच्यते तस्य तावच्छती संध्या द्विगुणा परिकीर्त्यते //
trīṇi varṣasahasrāṇi tretāyugamihocyate tasya tāvacchatī saṃdhyā dviguṇā parikīrtyate //
Here, the Tretā Yuga is said to last three thousand years; its twilight period (sandhyā) is stated to be of that many hundreds, and the concluding twilight (sandhyāṃśa) is declared to be double that.
It gives a technical time-measure for the yugas and their transitional twilights; such chronology is used to situate cosmic events (including pralaya) within vast cyclical time, though pralaya itself is not described in this verse.
By defining Tretā Yuga and its transitional periods, it frames dharma as time-conditioned: rulers and householders are expected to follow dharma appropriate to the yuga, with practices and standards shifting across these cosmic eras.
No direct vastu or temple rule is stated; indirectly, yuga-calculations guide ritual timing and the broader Puranic worldview in which rites, consecrations, and dharma-practices are contextualized by the age.