I'm just pointing out the danger of lowering that limit.
If a spammer manages to register and starts posting on a site. Let's assume they take 5 seconds to make a post (assuming they copy and paste something pre-prepared).
For a 30 second flood time, they can make 1 post every 35 seconds which is 102 posts in an hour.
For a 10 second flood time, they can make 1 post every 15 seconds which is 240 posts in an hour.
Definitely worth maintaining the higher flood time.