This issue was originally filed by @seaneagan

The intl package currently has unimplemented methods on DateFormat for this called formatDuration and formatDurationFrom. This is the wrong location for these APIs. Arbitrary DateFormat patterns don't match up to the corresponding CLDR data model.

The intlx package (http://pub.dartlang.org/packages/intlx) has DurationFormat which formats Durations, e.g. "5 minutes" or "5 min" and AgeFormat which formats DateTimes offset from now, e.g. "In 5 minutes" or "5 minutes ago" using CLDR data. See the following:

Demo: http://seaneagan.me/intlx/
Docs:
  http://seaneagan.me/intlx/docs/intlx/DurationFormat.html
  http://seaneagan.me/intlx/docs/intlx/AgeFormat.html

Proposal: move DurationFormat and AgeFormat to intl package and remove DateFormat.formatDuration/formatDurationFrom.