I have started my own research as to what day the GB took power and here is what I found
And then this site http://gwest59.tripod.com/ChristIsLord/id46.html says that the GB did the following adjustment
The last page of the February 1, 1976, Watchtower, was devoted to a notification entitled "Governing Body Adjustments." The article advised that the Governing Body had, as of January 1, 1976, formed six supervisory committees: Service Committee, Writing Committee, Publishing Committee, Teaching Committee, Personnel Committee, and Chairman's Committee. This was, of course, big news in the world of JWs. Prior to this time virtually all important policy- and procedure-making decisions depended ultimately upon the approval of one man--the Society's president, Nathan H. Knorr. The February 1 article did not elaborate, but it soon became clear within Brooklyn Bethel that these committees were now operating with a measure of authority that previously had been possessed only by Knorr. The president of the Society no longer wielded absolute, total control.
so it seems that Jan 1/ 1976 is when the GB had full control (read further in the above link)
To answer my own earlier question" on what day did the GB start to rule"
It seems they took power gradually like any dictator would.
The more I read on the internet about the WTS the more I realize how diabilical they are. The WTS is now more fragmented than ever before but the GB still has full control.
Did you know that the district of Brooklyn New york looses 10 million dollars a year to property tax because the WTS headquartes are tax exempt. There are some 3000 bethelites living in a compound there all connected by a tunnel system(the tunnels are owned by the WTS). The bethelites have to use the tunnels when traveling between buildings of the compound or they'll get stabbed. There was a recent stabbing there because a bethelite did not use the tunnel and he was found bleeding outside and a WTS ambulance loaded him up. Yes the WTS has it's own ambulance service. In fact they are a self contained unit that feeds off the estates of deceased widows and the gullable publishers (watchtower pushers at your door) who give any excess money they have into the contribution boxes at the kingdom hall.