I improved this. The max time between posts now changes depending on how many posts you have. If you have more than 100 posts, you can now post more frequently than every 20 seconds. The more posts you have, the lower the time, down to a minimum of 4 seconds.

Members with few posts now have to wait up to 6 minutes between posts. Does anyone know the best way to make it so that form data is not reset when hitting the back button? I think this happens just because the forum uses HTTPS. Can this behavior be changed?

I might actually increase this minimum time between posts later and increase the number of posts allowed hourly once the form issue is figured out.