When a Monarch dies, instantly the next Monarch is Rulling.
However.... Theoretically, they dont get to sit on the Throne until they are Crowned...quite often that can be some time after.
King Edward...the one married to Wallis, was NEVER Crowned...Technically speaking he never actually took possession of the Throne or Crown.
The Sixty years of Elizabeth is thus NOT dated from when she became Queen by Default...but when she was Crowned. The reason why this is important dates back to several things. Firstly, in times gone by there was often great dispute as to who was the next ruller. Look at William the Conquerer...promised the throne by the King...but the moment the King died, Harold decided that he was King instead.
Secondly, the whole reason of a Monarchy is that GOD himself has selected them to rule. GOD does this by a process known as Consecration, and believe me, having been one of very few people to actually witness a moment of consecration, I can tell you that it is very powerful. At the moment of a consecration GOD makes a person sacred unto him, in the same way he makes a Church Building sacred unto him, or a Grave yard. Instead of Hallowed ground, you have a Hallowed person. This happens during a ceremony where their is an annointing. At that Momment GOD himself has sealed the Monarch as the Monarch...until that point, they are not technically speaking sanctioned by GOD, only sanctioned by the States Tradition that there must always be a monarch, thus when one dies you move to the next.
So it is her Coronation, that we celebrate as the official start of her reign. Although technically, she Reigns the moment her predecessor is dead. This is an ancient Tradition that goes right back to the Bible. Zadock the Priest, and Nathan the Prophet annointed Solomon King. Hence why that quoted action from Scripture is one of only Two Coronational Anthems.
There is one thing that always happens during a Consecration...at the moment the act occures, the true character of the individual for a brief second is revealed. Now the whole ceremony was recorded for Queen Elizabeth...except for one part....the actual consecrational anointing.
She specifically requested a canope be used to hide her, and the Archbishop of Canterbury. For her, it was a personal and intimate moment between Her and GOD alone. Noone got to see the moment that GOD confirmed her Queen.
Hope that answers your Question.
Here are the Coronational Anthems
(I Was Glad)
(Catherines introit to marry Prince William was to the same music)
(Zadock the priest)
(Shows footage of the actual; event 60 years ago this weekend exactly) (The instruments she is given to hold are The Orb and Sceptors. Believe it or not, its most uncomfortable. She sits in an ancient wooden Chair which was the original British Throne, or as close as we can get, with a crown ballenced, and I do say BALLENCED on her head, its heavy. meanwhile she holds a heavy golden ball with a cross on the size of her head in one hand, and two golden wands in the other hand (both in the same) whilst wearing about twenty layers of heavy fabric vestments, that do feel and weigh like carpet.