The TimeToLive property is an integer value that specifies
the frequency in seconds at which the feed should be refreshed to
obtain updated information. Not all feeds specify a time-to-live, in
which case this property will have a value of zero.
The value of the TimeToLive property should be considered
advisory, and not all news feeds will provide this value. If the news
feed does provide this value, it is recommended that you consider it
to be the minimum interval at which you will poll the site for
updates to the feed.