Dow Jones business hours - when does the trading market open ?

When does Dow Jones index business hours starts ? Does it open for trading from 4:00 AM EST or 9:30 AM EST ?

Dow Jones standard opening hours are from 9:30 AM EST to 4 PM EST. There is also extended-hours trading, that is known as Pre-market trading or After-market trading (Post-market trading).

The trading hours are:

Pre-market trading hours - from 4 AM EST to 9:30 AM EST
Standard DJ trading hours - from 9:30 AM EST to 4 PM EST
After-market trading hours - from 4 PM EST to 8 PM EST