Surya Siddhanta
वारप्रवृत्तिः प्राग्देशे क्षपार्धे +अभ्यधिके भवेत्। तद्देशान्तरनाडीभिः पश्चाद् ऊने विनिर्दिशेत् ॥
A day of the week begins at the Des'ántara Ghaṭikás after or before the mid-night at the given place according as it is east or west of the Middle Line.
english translation
vArapravRttiH prAgdeze kSapArdhe +abhyadhike bhavet। taddezAntaranADIbhiH pazcAd Une vinirdizet ॥
hk transliteration by Sanscript