Surya Siddhanta
दिनक्षपार्धम् एतेषाम् अयनान्ते विपर्ययात् । उपर्यात्मानम् अन्योन्यम् कल्पयन्ति सुरासुराः॥
Their mid-day and midnight, which are opposed to one another, are at the end of each half-revolution from solstice to solstice (ayana). The gods and demons each suppose themselves to be uppermost.
english translation