To register a litter, anything from 3 days upwards depending on how busy they are.
To transfer ownership when you purchase a pup I've found within a week also, but at very busy times it can take upto 2 weeks it should never be longer than that either way, unless there has been a problem which you should be informed of. :-)
You can call the KC to ask about a registration if something is taking longer, they are very helpful. :-)