Hong Kong is 16 hours ahead of San Diego during standard time (or 15 hours during PDT). San Diego uses Pacific Time (PT, UTC-8/-7) while Hong Kong uses Hong Kong Time (HKT, UTC+8). When it's 12:00 PM in San Diego, it's 4:00 AM the next day in Hong Kong.
Hong Kong does not observe daylight saving time, so the difference varies between 15 and 16 hours depending on whether San Diego is on PST or PDT.
Best calling time: 5:00 PM - 7:00 PM San Diego time. This corresponds to 9:00 AM - 11:00 AM the next day in Hong Kong, catching morning business hours.
San Diego has significant trade connections with Asia through its port. The city's biotech industry has links to Hong Kong's financial sector. The time difference requires evening calls from California to reach Hong Kong's business day.