Shortnews are small messages that can only be displayed "one at a time" and only in the Complete version.
The Shortnews are used to display the same message (such as the Contact info) on several pages on the Website, or to pre-define a set of messages that can appear at a pre-defined time.
These messages could e.g. be that your company is participating at an Exhibition on a certain time. You could define one message that is displayed until the 31. January that tells your visitors that you will be at the Exhibition that starts on the 1st February and lasts until 6th February. (The Shortnews is set to appear from the time you write it until the 31. January)
The second Shortnews is set to appear on the 1st February and be removed on the 7th. This tells that you can be found in Hall B on the Exhibition.
On the 7th February the "Default" (usually the first Shortnews you wrote) will be the one displayed since the two others that were written for the periode until 7th February will have been automatically removed.
You can define if the Date and Time shall be displayed with the Shortnews. If this is a Shortnews that tells you that the "shop is open", it makes sense to show the date/time so that the visitors know that it is an updated message - and not just one you forgot to remove from the website.