[TYPO3-ttnews] cc_rdf_news_import - how to automate feed?

[Rico Zone]

Hi folks!
I am using Typo3 3.8 with the tt_news 2.3.6. Now I want to include a 
newsfeed with cc_rdf_news_import and xml_ttnews_import modules. I works 
beside the fact that it does not update the newsfeed automatically. I have 
to get the feed manually all the time.
As there is a "Reget after xxx second:"-option for cc_rdf_news_import 
-module I wonder if anyone is using this option as there seems to be more 
adjustments necessary because simply to write like 999 seconds does not work 
(and there is no documentation available).
Thanks a lot
Dirk