The article referenced just above gives more tips for ambiguous historical time zones.
If you're uncertain, send us an email at reports@cafeastrology.com with your full birth data for help. It's important not to alter the +/- of the entry. Keep in mind that the program converts local time to UT, not the other way around. An example of Time Zone Not Sure dates and locations occurs in the late forties and through the fifties in Illinois when an odd law was in effect regarding recording CDT times in CST. The Time Zone Not Sure field allows you to choose -6 for CST or -5 for CDT. The article referenced just above gives more tips for ambiguous historical time zones.