That ok as a suggestion - but I need an actual snail icon. Here is an example of my graphical skills:
Can somebody do better? It has to be an icon that looks reasonably well on different backgrounds. Icon height at most 16 pixels. Please don't suggest any icons from the web, the license there is usually unclear or incompatible.
Perhaps an hour glass icon might be a better choice as it wouldn't have to be that detailed and thereby would look less overloaded than the current snail icon. Additionally, I think it could be useful to mark slow filters in the list of blockable items (as well as in its tooltips), too.