SQ 995 then QF 219 at Changi
Medan → Singapore → London Heathrow
Timetable, Singapore time
23:05SQ 995 from Medan at the gate
23:10QF 219 to London Heathrow leaves the gate
5 min apart on the timetable
The last days
SQ 995 and QF 219 weren’t both flown 15 min to 12 h apart in the last 21 days.
Statistics from past flights, not live flight information. Always check times and your connection with your airline, and don’t base travel or booking decisions on these numbers.