Just filed this bug with Adobe. Hopefully they will fix it to provide better timezone adjust support. The current workaround is very unintuitive.
Update: Just to clarify, this is only about changing the second option (time zone adjust) in the adjust time dialog. There are a number of countries that work on 30m TZ offsets – Alaska, a number in South America, Middle East, the Pacific. There is a good table available on this page from the US Naval Observatory.
Concise problem statement:
Timezone adjustment does not support all timezones.
Steps to reproduce bug:
1. Attempt to adjust timezone by -7.5 hours (difference between New Zealand Daylight Time and Sri Lanka time)
2. Only 1 hour increments are available in the time zone adjust drop down combo.
Results: It is not possible to adjust the timezone in half-hourly increments. After some Googling, I found a very unintuitive workaround that involves selecting the first photo, and adjusting it by the required amount. This is not intuitive enough, and as there are 30 minute timezones, I believe obvious and intuitive support for 30 minute timezones should be included.
Expected results: In addition to the hourly TZ adjustment combo box, there should be another combo to the right that allows selection of 30 minute TZ by selecting either :00 (default) or :30 that is applied in addition to the TZ hour adjustment. This would make it possible to adjust the time to 30 minute timezones (e.g. Sri Lanka and India) in an obvious and intuitive manner.