The United States is a wide country with seven time zones. There are four time zones in the continental United States, each separated by one hour. When it is noon in New York City, is only 11:00 AM in Dallas, 10:00 AM in Denver, and 9:00 AM in San Francisco.

• Eastern Time (ET)
  Major cities: Boston, New York, Washington, DC, Atlanta, Miami
  10.5 hours behind India
  
  
• Central Time (CT)
  Major cities: Dallas, Chicago 
  11.5 hours behind India
  
  
• Mountain Time (MT)
  Major cities: Denver
  12.5 hours behind India
  
  
• Pacific Time (PT)
  Major cities: Los Angeles, San Francisco, Seattle
  13.5 hours behind India

US Time Zone Map

As suggested by the name, the time is changed by one hour twice a year so maximum daylight can be used. The sun rises very early in the summer. Therefore, the clock is set forward by one hour in summer. Daylight Savings Time (DST) moves one hour of daylight from the morning to the evening. That way, all activities start one hour earlier and maximum daylight can be used until later in the evening. Many people also get a chance to go out, play sports, etc., after work and enjoy the summer weather.

You should set the clock back by one hour on the first Sunday of November during the fall season and set the clock forward by one hour on the first Sunday of April during the spring season. Even though these are the general rules, in recent years, the government has changed the dates every now and then.

Remember the phrase: SPRING AHEAD, FALL BACK.

The time actually changes at 2:00 AM local time. It becomes 3:00 AM in the spring and 1:00 AM in the fall. However, as a practical matter, most people can just change the clocks before going to sleep the previous night or in the morning after getting up.

Please note that there are several regions in the U.S. that do not change the time, such as Arizona (except a small portion in Northwest Arizona called Navajo Indian Reservation). 

Until 2006, the state of Indiana didn't observe Daylight Savings Time. However, they follow the time according to the Eastern time zone (except a small portion near Chicago that includes cities like Gary).

Banks: 9:00 AM - 5:00 PM weekdays and 9:00 AM - 12:00 PM on Saturday. This may vary.
Post offices: 8:00 AM - 5:00 PM and 9:00 AM - 12:00 PM on Saturday. This may vary.
Stores generally open early in the east coast and are open later and later as you go towards the west coat. Some stores may be not open until 10:00 AM or even 11:00 AM, but they may remain upon until 6:00 PM or even 8:00 PM. Large shopping malls are open every day until around 9:00 PM with the exception of Sunday when they close at either 6:00 PM or 7:00 PM.

Convenience stores that sell food and other necessary items may be open 24 hours a day or late into the night.