Just to add that I too am finding this irritating. If your first search doesn't throw up what you want, you want to refine your search and run it again right away. The 30 second rule has been particularly tiresome today while I've been updating a lot of the links to other threads in an old post of mine.
While I absolutely can see the reasoning for flood control in making new posts, has FT ever suffering from someone "flooding" the search function? If so, fair enough, if not, and this is just a default that maybe hasn't been changed, please could you consider changing it?
Many thanks.