Using same code as https://confluence.ez.no/display/EZP/3.+Managing+Content#id-3.ManagingContent-UpdatingContent

Result:
=> modification date: ok
=> publication date: ko ..

Problem is due to $contentService->publishVersion() which call internalPublishVersion(). This method wait for a $publicationDate variable, of course not define with publishVersion(). So script give the current time ...