San Francisco — Silicon Valley's clock
San Francisco runs on Pacific Time (PST/PDT). Silicon Valley and the SF tech ecosystem operate on this clock — SaaS, venture capital, most consumer tech HQs are all here. Business hours skew later than East Coast (10 AM starts are normal, calls run to 8 PM PT). Time zone gap with India (13.5 h behind IST winter) drives most engineering handover calls to happen in the 8-10 AM PT / 9-10:30 PM IST window.