The listing of recent discussions works like this:

The first group are any threads you have marked as hot discussion. You can tell these by the box with the red X in it. You control how many are listed, or list none.

The next five are placed automatically. The first two of these are very recent threads that have 10 or less replies. The next three are recent threads that have more than 10 replies.

The hot discussion items stay until you remove them.

The first two of the automatic items will remain for at least 8 hours.

The last three remain for at least 24 hours.

Managers should think about the subject displayed. If a subject doesn't make much sense then click on the link and then use ChangeThreadAll to change the subject. Doing so will flush the cache of the old name and repopulate the home page list with the new subject.