The data hasn't been updated since 2004. Reading wikipedia, it seems that since that time https://en.wikipedia.org/wiki/Time_in_the_United_States for instance, Indiana implemented DST state-wide in 2006 but this data doesn't reflect that, for example

>>> import pyzipcode
>>> zpdb = pyzipcode.ZipCodeDatabase()
>>> zpdb[46222].city
'Indianapolis'
>>> zpdb[46222].timezone
-5
>>> zpdb[46222].dst
0

But this is no longer true, Indianapolis does observe DST, its Wikipedia article says as much:

Time zone - UTC−5 (EST)
 Summer (DST) - UTC−4 (EDT)

https://en.wikipedia.org/wiki/Time_in_Indiana

You could throw out this data and instead calculate it in import_zipcodes.py using https://pypi.org/project/timezonefinder/ , but then you have to do regular releases. Another option would be to make it an optional dependency and if people install pyzipcode like pip install pyzipcode[timezonefinder] then you could use a .timezone property which would be calculated on the fly from the coordinates.