If you were trying to hose a competitor by posting e.g. their blog posts at a slow time like 4 am pacific, they'd have to help you out by publishing their blog posts at that time. In my experience no one does that. Companies wait to publish their posts at good times, and then the links are quickly submitted to HN, either by the company or someone else. So a bad guy would rarely have an opportunity to submit an as-yet unsubmitted link at a slow time.