how long do transfers take on these items
That depends.
Anything other than a 12.3 and the transfer should be fairly quick.
With 12.3's the RCMP insist the gun go to their lab to be inspected and certified that the conversion is to their standards. That process can take up to several years and there is no fixed time limit so they could take as much time as they want and you have little recourse. Hence 12.3 guns aren't really a good purchase at this time.
One question I've never heard answered is that if a 12.3 has already gone through the RCMP lab process and gets sold again, does it have to go back and be rectified again? Like every time the thing gets sold?