Alfirin's analysis is a thing of beauty, and I will rep you for that post, when I can.
I guess to answer why Saruman hadn't acted before the WK arrived - now keep in mind this is my own rambling speculations - I have nothing as far as "proof."
I think we should keep in mind that dangerous game Saruman was playing. He was not only deceiving Gandalf, and the rest of the Wise, into trusting him, but he was also trying to deceive Sauron. Saruman wanted to be the Ring Lord himself, he had to not only appeal to Sauron, but keep the trust of the "Wise." And when Elrond, hears of Saruman's betrayal, he is completely shocked (as was Gandalf).
As Gandalf says in
The Council of Elrond, even the greatest spiders leave a "weak thread," and Sarumans lies begin to unravel. When he's caught, he's got himself stuck in a vice; Gandalf comes after him to expel him from the Order and the Council, Sauron is after the presumed Hobbit that he captured.
So, for Saruman, he was playing such a dangerous game, he had to keep up the act as long as possible. As Grishnakh says Sauron knows Saruman is "treacherous" and "the Eye is on him." (
The Uruk-hai). My guess is Sauron had his eye on Saruman from the very beginning. Saruman might have thought he was keeping his true intent hidden, and Sauron might not have figured it out until later, but he definitely had Saruman under surveillance from the get go.
Remember, that it was Saruman who is credited for driving Sauron out of Dol Guldur, and it is Saruman who did it to prevent Sauron from searching The Gladden Fields. This wasn't a loyal, trusting friendship, and I very highly doubt Sauron and Saruman went to counseling together to work our their past.
Long story short, Saruman wanted to keep the Ring away from Sauron, just as much as he wanted it for himself. Had he gone racing off for the Ring when he first got news of where it probably was, this would have certainly tipped Sauron off sooner. On where the Ring was, and also Saruman's own treachery. Not only that, but the good guys would have learned about Saruman's betrayal a lot sooner than they did, when Gandalf spilled the beans (what a tattle tale!
). In a way, Saruman handcuffed himself, by the way he decided to play the game.