Parts of Indiana have the same issue. Notice I said parts and not all - there are parts of Indiana that observe DST because they border with states observe DST

Parts of Indiana have the same issue. Notice I said parts and not all - there are parts of Indiana that observe DST because they border with states observe DST and it's to their advantage to stay in the same time zone. What a mess! Just makes writing software that much more difficult! That's why in the utility business it's common to use the language of standard time, daylight saving time, and prevailing time. For the Eastern timezone they write it as EST, EDT, EPT respectively. The important point is EST and EDT never vary - they'e fixed offset from UTC (UTC-05:00 and UTC-04:00, respectively). EPT is the squirrelly one - sometimes it matches EST and other times it matches EDT. At least when processing a time interval you know whether you have to take clock movement into account.