Brihat Samhita
अर्धास्तमितानुदितात्सूर्यादस्पष्टभं नभो यावत् । तावत्सन्ध्याकालश्चिह्नैरेतैः फलं चास्मिन् ॥ ३०-०१ ॥
That period which precedes the moment when the Sun has just half risen and that which succeeds the moment when the Sun has just half set, during which the stars are invisible is known as Sandhyākāla or twilight period. From the peculiar indications of this period effects may be predicted as follows.
english translation
ardhAstamitAnuditAtsUryAdaspaSTabhaM nabho yAvat । tAvatsandhyAkAlazcihnairetaiH phalaM cAsmin ॥ 30-01 ॥
hk transliteration by Sanscript