There are many ways to navigate through time. To get started you can simply swipe through a few months and pick any day; once you pick a day Time Jump will show you the 'time difference' between the dates.
When you need to jump to a certain date in the past or the future, just tap either of the large date icons and a standard date picker will allow you to set either date directly.
Time Jump starts up with both calendars set to today's date. Today's date is displayed in the middle - anytime you need to reset both calenedars to 'today' just tap 'Today'.