Apply filter instead of *delaying* page

[glaebhoerl]

What I'd like: When I navigate to a site in the block set, a filter (e.g. blur) is applied for (e.g.) 5 seconds, after which the site can be used normally.

Why I'd like this: The page will already be loaded once the timeout expires. Applying a filter is much less 'invasive' and less likely to have unfortunate interactions with other addons or browser or website features. (I don't remember exactly what interactions I encountered, but I do know I switched to using filters exclusively because of them - which however only support blocking and not delaying.)

Importance: Nice-to-have. If it's simple to implement, I might even take a shot at it myself, given some pointers w.r.t. the relevant code and how the feature should be exposed. If it needs a major architectural revamp, probably not worth bothering with (for my sake anyway).