London is typically 8 hours behind Hong Kong. When it's 5:00 PM in Hong Kong, it's 9:00 AM in London. Hong Kong does not observe daylight saving time, but London does.
During British Summer Time (late March to late October), the difference is 7 hours. During UK winter time, the difference increases to 8 hours.
Optimal meeting window: 8:00 AM - 11:00 AM London time (3:00 PM - 6:00 PM Hong Kong, or 4:00 PM - 7:00 PM in winter). Morning London catches afternoon Hong Kong.
London and Hong Kong have historic financial ties, with London's morning session overlapping with Hong Kong's afternoon trading hours.