I wonder how long it took for the commonwealth to validate the abdication?
According to a BBC timeline, pretty quickly.
On Nov 15 1936 Edward first told Baldwin of his intent to marry Mrs. Simpson; Baldwin replied that whomever the King marries becomes Queen and that the public would not accept Mrs. Simpson. Edward first says that he is prepared to go.
On Nov 25, Edward again calls for Baldwin and tells him he wants a morganatic marriage. He authorizes Baldwin to raise the matter with the Cabinet and commonwealth. Within 7 days (Dec 2) Baldwin returned to the King telling him that the cabinet and commonwealth rejected such a marriage.
9 Dec - Edward notifies government of his intent to abdicate.
10 Dec - Edward signs Instrument of Abdication. Baldwin informs the Commons.
11 Dec - Abdication endorsed by Parliament. Edward abdicates and George VI becomes King
10 Dec - 12 Dec - all the commonwealth realms approved the abdication (either their legislatures if they were in session, or governments)
So the whole actual process took about 2 to 2 1/2 weeks. Pretty remarkable when you think of it.