Why are there so many timing options that allow EST?

I need to add the ability to change time zones for North America only. A total of six time zones, including Hawaii and Alaska.

I am in the eastern United States, so my time zone is eastern. Choosing the time zone for my location, I can choose New York, Chicago and several others. I'm not sure why there are so many different time zones that allow the same offset; if due to DST.

All I'm basically looking for is these six zones:

  • Est
  • Cst
  • MST
  • Pst
  • AKST
  • Hst

Can someone tell me why there are so many different time zones to choose from this solution for the same offset?

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