this app has things to recommend it, but it also has a significant bug that prevents it from achieving its potential. If you've selected a city to calculate time with that is across the international dateline from your actual location, the day/date shown on the date/time selection wheel reflects the day for your current, physical location, rather than the city selected. When you tap the "close" button, iTimeZone then calculates the wrong day for all cities in the list.
For example, I'm in the MST time-zone (Denver, CO). It's Monday, 4/25. I've been told that I have a meeting with someone in Seoul, South Korea on Wed., 4/27 at 9:30AM their time. I double-tap on Seoul in the list, moving it to the top and making it the active city. I tap the time button, use the wheels to select Wed., 4/27 at 9:30AM, then tap close. iTimeZone then calculates the times incorrectly, displaying the time/date of my meeting in Seoul as THURS., 4/28 at 9:30AM, and time in Denver as WED., 4/27 at 6:30PM. The time of day is correct, but the day of the week is completely wrong - it should be Wed. in Seoul and Tues. in Denver. If I do this calculation the other way, working with the time in Denver (my physical location) instead, it can do it properly.