अधोलोकवर्णनम् (Adholoka-varṇana) — Description of the Lower Worlds and Cosmographic Measures
संध्या मुहूर्त्तमात्रा तु ह्रासवृद्धिस्तु सा स्मृता / लेखाप्रभृत्यथादित्ये त्रिमुहूर्त्तगते तु वै
saṃdhyā muhūrttamātrā tu hrāsavṛddhistu sā smṛtā / lekhāprabhṛtyathāditye trimuhūrttagate tu vai
Sandhyā lasts only a single muhūrta; that itself is remembered as the measure of decrease and increase. And in the course of Āditya, reckonings such as “lekhā” are taken when three muhūrtas have passed.