I've been very interested in this problem. I ran a community for a few months that wound up being quite popular (40k uniques a day before I closed it down). My attempt to address with problem was to have a min + max time, but most interestingly count the number of posts as well. Even if an opinion was popular if it got a response out of people it would stay around longer before dropping of quicker.

I prioritised community engagement over the communities quality of content. This turned out to be slightly more effective way of ranking content.