[IvorETower]

It's detected by the camera near the rear view mirror so the changes are immediate (as soon as the camera has read what it thinks ais a new speed limit sign).

Interestingly I raised a question on another forum... does the car know in which country it is, and whether the signs are in mph or kph? If you find a French-registered Captur, for example, doing 30mph in a 50 zone, it may be because it's recognised the 50 sign byt interpreted it as 50kph. Conversely if you take a UK-registered Captur to France and drive on the autoroute, you may find that you can travel at 110 or 130 mph.......

 

[IvorETower]

The car doesn't switch to the "default" limit for the road, it switches to the speed limit sign that the camera has read, or mis-read - and it's instantaneous when the camera reads the sign.
See elsewhere- we appear to have established that if you take the car to France for example but leave the speedo in MPH, then when the camera reads a "110" sign on the motorway,, it will advise that is the limit in MPH and will let you get to 110 MPH before it flags up that you have exceeded the speed limit