Just noticed a bug...
The last refresh time is incorrect for Arizona zip codes. Appears to display MDT, not MST. Arizona does not use Daylight Saving Time (except for the Navajo reservation in NE AZ, which does follow it...).
Good catch, thanks! Problem is fixed for the most part, but there will probably be some zip codes that still behave poorly... I'm at the mercy of the database creator with this one!