I work with people all over the world and it's useful to know in advance what time it is where they are to schedule voice and video calls. Frankly, it's not that complex. The basic iOS Clock app has that covered. Or you could just ask Siri. And there are an endless number of apps that can help you visualize the time difference. Somehow Chronulator manages to make the task of figuring out the time somewhere else a real trial. This free app requires iOS 6.1 or later and is compatible with iPhone, iPad, and iPod touch. This app is optimized for iPhone 5.
Here's a test: using the main display from the Chronulator app, tell me what time is it in London?
Chronulator uses a large dial set on a black background and displays city or location names as some sort of curved flag or banner. Some, but not all of the locations also include a thin line connecting to a 24-hour clock around the dial's face. The banners make it difficult to quickly glance at the display and determine what time it is in various locations. That defeats the purpose of the app. The app is made even more confusing for those of us who do not think in a 24 hour or "military time" clock. That's another conversion you have to do in your head (what time is 1500 hours?). Yes, I can do math, but the point of an app like this is to make it easy to see what time it is somewhere else, not calculate it.
For fun, here's the same display with the app's maximum of 7 locations:
I still don't know what time it is in London. You can touch this display dial to turn the clock, so to speak, and see what time it will be in Tokyo when it's 2 P.M. where you are. Apparently you will still be unable to tell what time it will be in London. It's also confusion that Zero hour (12 A.M.) is at the bottom of the dial, not the top.
I don't find this app to be useful. I find it much easier to just ask Siri, "What time is it in Tokyo?"
Frankly, you don't need any 3rd party apps for this. If you want to see the times in multiple world cities just use the built in iOS clock, which you can quickly display by sweeping up from the bottom of the screen. It's a clean, easy to understand display and it's built right in.
Don't bother with Chronulator. There's enough confusion and ugliness in life as it is.