<xt:countdown format="FORMAT" from="NOW 1" to="NOW 2"/> FORMAT=years months days hours minutes or seconds
NOW 2= now yesterday today tomorrow
or a date in mm/dd/yy/ or dd month yy form
or a time hh:mm:ss
and it seems just about any other way you can describe a date or time!
The parser also understands timezone names ie. BST PST UTC etc and things like "last tuesday"!