"My plan is to assign the prescaler to the RTCC and spin waiting for
    it to equal zero."

That works; my usual technique is to set the RTCC to a negative number
and bit-test the MSB.  Remember to account for the delay between
initializing the RTCC and when it begins to increment.

                                Paul Milazzo <milazzo@bbn.com>
                                BBN Systems and Technologies
                                Cambridge, MA