Here's the output of a ./Build test after various fixes. There is some warning about a string comparison happening where it's expecting an integer. My guess is some back-end store is returning a formatted date rather than an epoch time.
Argument "\x{32}\x{30}..." isn't numeric in numeric lt (<) at /home/www/paulm/openguides-trunk/blib/lib/OpenGuides/Feed.pm line 169. Argument "2006-10-28 19:02:59" isn't numeric in numeric lt (<) at /home/www/paulm/openguides-trunk/blib/lib/OpenGuides/Feed.pm line 169.
("\x{32}\x{30}..." is "20...")
This IMO really should be a failure via an assertion further back up the stack.
Looking at the Wiki::Toolkit pages the closest the format of last_modified gets to being specified is as a "timestamp". (So the bug is that it's not really nailed down.)
There's a bunch of XML issues in the paste someone might have thoughts on too.
Paul