Since After until

The value of the since attribute is intended to contain the lower bound of items contained within the feed.

The value of the until attribute is intended to contain the upper bound of items contained within the feed.

Ensure that both of these values are represented in a manner that allows string collation by subscribers to yield the appropriate results. For example, if the publisher uses a date-time value to represent an incorporation timestamp for since and until, the value MUST be normalized for string comparison (e.g. 2006-05-02T09:10:33Z instead of 2 May 2006 09:10:33)

If these values are reversed, simply swap them.