What features are included in the paid version of the app?
The premium version of the app has an online time zone lookup feature which allows you to find the time for anywhere in the world. It also has a time zone calculator, being able to see the time to the second, a sync with Apple Watch, the ability to set a calendar appointment using the app, custom themes for the app and the widget, and no ads.
You can read more about the features of the app and see screenshots on the App Store.