अधोलोकवर्णनम् (Adholoka-varṇana) — Description of the Lower Worlds and Cosmographic Measures
मध्याह्नस्त्रिमुहूर्त्तस्तु तस्मात्कालश्च संगवात् / तस्मान्मध्यन्दिनात्कालादपराह्ण इति स्मृतः
madhyāhnastrimuhūrttastu tasmātkālaśca saṃgavāt / tasmānmadhyandinātkālādaparāhṇa iti smṛtaḥ
Midday lasts for three muhūrtas; the time after saṅgava is called madhyandina. After the madhyandina period, the time is remembered as aparāhṇa.