I lived near a main road that quickly moved from 55 to 45 then to 35. Nobody, and I mean N*o*b*o*d*y would slow down. The cops didn't bother pulling people over in that area, I'm pretty sure they gave up years ago. Luckily I've never been pulled over for not slowing down. I usally Never do. I would assume that as soon as you pass the sign your vehicle should be doing that speed.
Hopefully if I do get pulled over for not slowing down, it will be because I am truly unaware of the decrease in speed.
Wow, those signs can be badly placed.