For my work with MacStories, Connected, and Virtual, I need to account for a variety of time zone differences: whether it's a quick chat on Skype with the MacStories team, setting up a recording time for an interview, or scheduling posts for the site, I find myself converting time zones for Italy, New York, San Francisco, Australia, and the UK on a daily basis. Over the years, I've learned to do the math manually and remember when it's time to switch to daylight savings time, and I've also started using apps like Living Earth and iStat Menus on the desktop to have a glanceable list of world clocks. Time Zones simplifies this concept even further and adds a couple of features that I haven't found in other apps.
Time Zones is simple and clear: time for your current location is displayed at the top and locations are listed below. You can search and add thousands of locations from the app's Add menu, and the background of the main screen is colored after the time of the day, which is a nice touch. Each time zone can display offsets, times in AM/PM formats or 24-hour clock, and you can rename locations to have more descriptive names.
My favorite feature is Quick Check, which lets you pick a specific date and time and see how it will convert across your favorite time zones. Because I often receive requests to publish reviews at, say, “8 AM San Francisco time”, Quick Check works well for this type of conversion as it can set a time for that location and compare it with other cities configured in the app. I wish that the app could also accept time zone names (which I never managed to learn) instead of just geographical locations, but that would probably make the app less intuitive and skewed towards a more professional use case, which doesn't appear to be the focus in this 1.0 release.
Time Zones is sharp and effective. The app is supported by modal ads that can interrupt the experience, but they're easily dismissable if you don't want to pay $4.99 to remove them. Time Zones is available for free on the App Store.