Hong Kong and Beijing are in the same time zone. Both cities use UTC+8 (Hong Kong Time/China Standard Time). When it's noon in Hong Kong, it's also noon in Beijing.
Neither city observes daylight saving time.
Any time works! Since both cities are in the same time zone, scheduling is never an issue.
Hong Kong and Beijing are connected by high-speed trains taking about 9 hours, as well as frequent flights taking about 3 hours.