सूर्यरथ-कालचक्र-आयनविभागः, संध्योपासनम्, देवयान-पितृयानम्, विष्णुपद-गङ्गावतरणम्
उषा रात्रिः समाख्याता व्युष्टिश् चाप्य् उच्यते दिनम् प्रोच्यते च तथा संध्या उषाव्युष्ट्योर् यद् अन्तरम्
uṣā rātriḥ samākhyātā vyuṣṭiś cāpy ucyate dinam procyate ca tathā saṃdhyā uṣāvyuṣṭyor yad antaram
रात्रि को ‘उषा’ कहा गया है और दिन को ‘व्युष्टि’ भी कहा जाता है। तथा उषा और व्युष्टि के बीच जो अंतराल है, वही ‘संध्या’ कहलाता है।
Sage Parāśara (in instruction to Maitreya)
This verse defines saṃdhyā as the interval between night (uṣā) and day (vyuṣṭi), highlighting it as a liminal, sacred turning-point in the daily cycle of cosmic order.
He explains time through precise naming: night is termed uṣā, day is termed vyuṣṭi, and the transitional interval between them is saṃdhyā—showing that cosmic time is understood through structured thresholds.
Even without naming Vishnu directly, the verse supports the Purāṇic view that orderly time-cycles are a manifestation of the Supreme Reality’s governance—Vishnu as the sustaining principle behind rhythm, law, and continuity in the cosmos.