Matsya Purana — Glory of Tīrtha-Śrāddha: Best Times
सायाह्नस्त्रिमुहूर्तः स्याच् छ्राद्धं तत्र न कारयेत् राक्षसी नाम सा वेला गर्हिता सर्वकर्मसु //
sāyāhnastrimuhūrtaḥ syāc chrāddhaṃ tatra na kārayet rākṣasī nāma sā velā garhitā sarvakarmasu //
The late-afternoon period of three muhūrtas is called sāyāhna; one should not perform śrāddha at that time. That time-period is known as “Rākṣasī” and is censured for all rites.
This verse does not discuss pralaya; it focuses on dharma in the form of ritual timekeeping, warning that certain periods are ritually unsuitable.
It instructs householders (and by extension kings who uphold public dharma) to observe proper muhūrta discipline: śrāddha should not be done in the sāyāhna trimuhūrta, preserving ritual correctness and social-religious order.
The significance is ritual (not architectural): it identifies an inauspicious time-slot called Rākṣasī velā and prohibits performing śrāddha (and broadly discourages rites) during it.