Reduce your comment spam with comment timeout. This plugin automatically disables comments on older blog entries after a certain period of time. It also gives you an option to automatically keep them open for longer wherever there is an ongoing discussion. This WPMU Edition is modified by Patrick Chia based on James McKay Comment Timeout
Active discussions can be kept open after the cut-off You can set it to keep discussions open after the cut-off time where there have been recent comments. You can limit the length of a discussion You can optionally set it to close the discussion after a certain number of comments have been posted. Pages, trackbacks and pingbacks can be included or excluded You can apply it to pages and/or trackbacks and pingbacks as well as posts — or not if you prefer. Site Admin Configuration page You can configure how long you want to keep comments open on the site administration. Control by site administrator not your blogger. It doesn’t alter the database Comments are automatically closed without changing the status of the post in the database. If you deactivate this plugin, comments on your blog will be re-opened.