Thirteen and a half hours, then twelve and a half
San Francisco keeps Pacific Time, UTC−8, and moves to UTC−7 from the second Sunday in March to the first Sunday in November. India does not move. So a 09:00 start in San Francisco is 22:30 IST in winter and 21:30 IST in summer, and the city's working day ends in the Indian early morning.
That leaves an Indian team three honest choices. Staff a night desk that works the San Francisco day; hand over between an evening and an early-morning shift in India; or answer the next Indian morning and rely on the 24-hour window, which a question from 14:00 in San Francisco keeps open until 14:00 the next day, 02:30 or 03:30 IST.
The third option suits low-volume accounts. Customers who pay for support in their own hours usually expect the first or second, and a WhatsApp number that only answers twelve hours later is worse than none. Decide before you print the number on an invoice.