I have not really investigated the what problem in the code is so I am not sure what things should be set to. I set my GMT offset to to get right (+9) and my posts started showing right then changed $hours around until I got freshness right in my case it was -18, but all I can suggest is get the post time right by changing $bb->gmt_offset and then use $hours to bring freshness time into line. This plugin is really only a tempory fix till later beta version bbpress fixes the code properly.
I wrote a quick plugin to correct this it is at
http://www.ryuuguu.com/wordpress/2006/12/22/correcting-bbpress-freshness-1/
you will need to edit
$hours=-18;
[code]
to find the right number for your offset
[code]
$hours=-18;
to find the right number for your offset
[code]
to find the right number for your offset
