I am guessing you are not from the USA. There are more than 3 time zones. We have some where between 7 and 9 depending on how you count, and what you count as the US. Several states have split time zones, and because we like things complicated here in the US, I live in a state that doesn't believe in DST (Arizona), but often gets a separate listing in time zone tables. And there is a section inside the state (the Navajo Nation) that does honor DST, and a section inside that (The Hopi nation) that doesn't honor it.
There. That should clear things up.