Jatakaparijata 9.59

9.59

ṛkṣasyānte bhavedrātrāvādau yadi dine tathā |
saṃdhyāsu ṛkṣasandhau tu tadetad gaṇḍalakṣaṇam ||

At the end of an asterism if at night, at the beginning if by day, / and at the junction of asterisms during the twilights: such is the definition of gaṇḍa.