I got this to work by creating a temp directory under the plugins directory and changed the svn to this. I made the temp directory because they would not download directly into the plugins directory due to the originals coming from the branches.
svn co http://svn.web-wack.at/ispconfig3_roundcube/trunk/
Then copied them over the existing ones in the plugin directory and now the date/time entries work.
Back your directories up first as I am using RC 4