upgrading from PAL -> RPAL was faster for me than originally getting my PAL, since the mandatory 28 day waiting period does not apply the second time around.
Since I am in Ontario, the longest portion of the upgrade process was waiting to receive my stamped restricted test results back from the CFO. Once the test results were in, I think the wait was somewhere in the range of two weeks. I was interviewed, along with both my references, on the same day so there was no "added delay" for the interview process.
If you're not in Ontario, you're far ahead of those of us who are.
There is an excellent sticky in the Newbie FAQ section on streamlining your PAL application. Read the whole thing, it's your shortest path to success.