Of course, you don't become evil overnight when falling from the post like Saruman had. I think we can see - as you have very nicely displayed here, Boromir - the "chart" of his fall, generally, in the points of a person (or spirit) a little bit proud of himself (in Valinor) => jealous on Gandalf (also in Valinor, that famous "not-as-the-third" thing; but enhanced after the arrival by knowing about the Ring Gandalf recieved) => growing in being proud (when seeing those stupid Middleeartheans, and also after recieving the Keys to Orthanc) => becoming lusty for power (after settling down at Isengard) => growing more selfish and more centered and closed at himself (like Treebeard said, also coming from how he lived at one place - he changed caring about outside world and the life in the world around him for caring only for his own agenda, literally he changed "change for cold comfort"
) => falling to the lure of power to that point that he started to lust for the One Ring itself (around 2851) => definitely changing his heart and secretly plotting AGAINST his former allies (! to this moment Saruman might be selfish or whatever, he might even been thinking wrong about Gandalf&co, but he didn't DO anything against them - now we have here lying to the Council, fortifying Isengard - 2953, spying Gandalf and putting down spies in the Shire) => hooking up with Sauron (c. 3000 - after using the Palantír of Orthanc). The rest we all know, I suppose.
But back to the original question - in the light of this what we stated above, when do you think, that Saruman actually started to SMOKE?