Check out https://pub.dev/packages/instant#-readme-tab- for Instant's pub page.
Instant's primary purpose is formatting of dates and times, but it provides a number of features to provide a seamless integration with the normal DateTime interface:
Current DateTimes in any timezone worldwide.
Easy and customizable formatting of dates and times into Strings.
Methods for formatting with current local DateTime, as well as with user-provided DateTimes.
Calculate difference between two DateTimes in years, weeks, days, hours, minutes, seconds, and milliseconds.
Provide a Stopwatch class that is a) not asynchronous and b) less memory-intensive