Surya Siddhanta
सुरासुराणाम् अन्योन्यम् अहोरात्रम् विपर्ययात्। तत्षष्टिः षड्गुणा दिव्यम् वर्षम् आसुरम् एव च ॥
An Ahorátra (day and night) of the Gods and that of the Demons are mutually the reverse of each other, (viz. a day of the Gods is the night of the Demons; and conversely, a night of the Gods is the day of the Demons). Sixty Ahorátras, multiplied by six, make a year of the Gods and Demons.
english translation
surAsurANAm anyonyam ahorAtram viparyayAt। tatSaSTiH SaDguNA divyam varSam Asuram eva ca ॥
hk transliteration by Sanscript