Matsya Purana — Measures of Time: Caturyuga Computation
चत्वारिंशत्सहस्राणि मनोरन्तरमुच्यते मन्वन्तरस्य कालस्तु युगैः सह प्रकीर्तितः //
catvāriṃśatsahasrāṇi manorantaramucyate manvantarasya kālastu yugaiḥ saha prakīrtitaḥ //
The interlude between Manus (manorantara) is said to be forty thousand (years). Thus is proclaimed the duration of a Manvantara together with its Yugas.
It frames creation and dissolution as recurring, measurable cycles: Manvantaras proceed with Yugas, and even the transition between Manus (manorantara) has a defined duration.
By emphasizing long cosmic cycles, it encourages dharmic steadiness—kings and householders should act with a sense of time-tested order (yuga-dharma), not short-lived impulse.
No direct Vastu or ritual procedure is stated; the significance is indirect—ritual calendars and temple traditions often align observances to yuga/manvantara concepts taught in Purāṇic chronology.