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As far as I know the news module was not designed to be compatible with PHP5 . It was made before PHP5 had a final release, and I haven't seen an upgrade since then.
From your description it looks like something has been changed with the way timestamps are handled in PHP5.
To solve your problem I guess you'd either have to go back to PHP4.x or debug the news module with regards to the changes brought about in PHP5
I'll take a quick look, but I suspect that will be a huge job... and I believe Hervé is very close to finishing and releasing News 1.3, so your problems might have been solved with that release.
Of course, I could be on the wrong track entirely with my belief that it's related to PHP5 issues... just offering my opinion, it doesn't help you much but it's better than no response, I guess...
Rowd
edit: After reading your post again, could it be that your server has a different date to what you are expecting? Does changing the site and/or user preferences for timezone change anything?