Was it something that slowly built up over time? Was it all at once? Were people talking seriously about revolution 20 years in advance, or would such ideas have been dismissed as ridiculous?
I'm interested in the same for other major revolutions as well, if someone feels more qualified to answer on those fronts.
More than 20 years. At least 30.
The thing to remember is that the population of the colonies was basically doubling every twenty years. At that rate, even if it started tapering off, it wouldn't be long before there were more people in the colonies than in Britain and it's silly to think they would put up with being ruled from London for London if they could help it. On this basis the French colonies in Canada were considered useful for the British Empire. With them as a threat the British colonies needed the security of the mother country.
This is all from Theodore Draper's A Struggle for Power. This is the opening concept of the book. It starts right on the first page. Draper traces the idea through the pamphlet war of 1759 (over whether to give Canada back to the French after the Seven Years War was over) and back to famed Swedish naturalist Peter Kalm who recorded hearing it from colonists in 1748.
But it's one thing to point out that at some point in the not too distant future the colonies were in all likelyhood going to separate from Britain and quite another to think it's time to get ready to start rebelling.
A fun fact on the American Revolution: the majority of Americans were were either opposed or neutral in regards to breaking ties with Britain. Only about 40% favored the revolution. Granted, that is still technically a majority of the population, but it does help illustrate the fact that not all Americans were gung-ho for war. Additionally, it was the financial support of the French (to spite the British) that helped the United States survive the war, and the French overspending to aid the U.S. would lead to massive debt for the French Monarchy, and ultimately the French Revolution.
But to better address your question, Thomas Jefferson was a huge admirer of the French philosophes of the Enlightenment, an era where, among myriad other philosophical topics being debated, many ideas for new political systems were also being discussed, including constitutional democracy. From here, I think the connection between the French and the United States begins to become even more evident: the ideas coming out of France during the Enlightenment helped form the U.S. government; Jefferson, among other prominent founding fathers, were frequent visitors to Paris and guests of the French monarchy; money coming from France helped fund the new idealistic country, and so on. Louis XVI of France, who provided the financial assistance, was so proud of what French ideals (and money) had accomplished, he had copies of U.S.documents such as the Declaration of Independence translated and distributed throughout. Considering what happened to him and France not long after, I personally have to question his logic here.
A lot of modern Americans tend to view the Revolutionary War as an isolated U.S. vs. Britain conflict, but events in Europe, such as the Enlightenment, paved the way for the Revolution. Likewise the American Revolution had massive ramifications in Europe, such as the aforementioned French Revolution, which led to Napoleon, which lead to the beginnings of German unification... You can see where this is going.
EDIT - Sources: Senior History Major, so this was pretty much day one stuff as far as U.S. and European history goes, so.. grab a survey-level textbook for either class? I can drum up sources if needed, though.