AI 640 then SG 622 at Mumbai
Chennai → Mumbai → Varanasi
Timetable, Mumbai time
12:50AI 640 from Chennai at the gate
10:40SG 622 to Varanasi leaves the gate
21 h 50 apart on the timetable, overnight
SG 622 leaves 21 h 50 after AI 640 arrives on the timetable: more than half a day, so not a connection we count.