The house has to approve, maybe even pick the VP? I could see the house, picking a Republican, if they had half a brain. Maybe Trump?
First Nixon appointed his VP, Gerald Ford (Ford served eight years (1965–1973) as minority leader), which both chambers overwhelmingly voted to approve.
25th Amendment Section 2:
“Whenever there is a vacancy in the office of the Vice President, the President shall nominate a Vice President who shall take office upon confirmation by a majority vote of both Houses of Congress.”
There is no time limit minimum or maximum required for this action.