The US market runs on a different clock and a different structure from the one Indian investors know. Regular trading is 7:00 PM to 1:30 AM IST while US daylight saving time is in effect (March to November) and 8:00 PM to 2:30 AM IST the rest of the year — the hour shifts twice a year, which catches people out.
Structurally, it helps to keep two things apart that are often confused. NYSE and NASDAQ are exchanges — venues where shares change hands. The S&P 500, the Dow Jones Industrial Average and the Nasdaq 100 are indices — measurements of baskets of shares. A company listed on NASDAQ may well be in the S&P 500; the two facts are unrelated.
The articles here cover the timings in practical terms, the exchange-versus-index distinction, and how a US brokerage account also opens the door to European, Japanese and emerging-market exposure.