Thanks to a suggestion by Daniel of Southern Cross Ventures, FeedDigest now has a tag which will tell you how long ago an item's date was in the past (or on some broken feeds, when in the future!). So, for example, instead of simply listing the date with each item like "20th February, 2005".. if you use %TIMEAGO% in your template, you could get "67 days and 5 hours ago".
%TIMEAGO,FULL% gives you the most precision, e.g. "5 years, 2 days, 12 hours, 7 minutes, and 3 seconds ago"
%TIMEAGO% gives you middling precision, e.g. "5 years, 2 days ago"
%TIMEAGO,SHORT% gives you the least precision, e.g. "5 years ago" or "2 days ago" or "2 minutes ago"
Simply manually edit your digest's template from the control panel, and you can begin using this feature immediately.
Please note that %TIMEAGO% will not be up-to-the-minute accurate due to FeedDigest's caching. Depending on how often the items in your digest change, and the level of our caching at the particular time, times between updates will vary.