New ideas go through three stages. Stage one is discovery. Someone has to actually come up with the idea. The time for this is from the start of history up until the idea is formed.
Stage two is peculation. The idea needs to spread through society. This can take almost any amount of time. I recall hearing about three cases, one that took seven years, another that took seven days, and a third that took just seven hours. The first was the American independence. It's 1769, and someone in Boston asks a man in the street if he thinks America ought to declare independence from Britain. The man looks at the questioner like he's nuts. "Independence? But, I'm British!" Seven years later, his answer is different. "Hell, yes-- we're Americans!"
In 1986, Marcos had ruled the Philippines for decades. Every effort to get rid of the dictator failed, and it appeared he would be in power forever. The entire country was resigned to this fate. Then, people in the streets started chanting for him to leave. Seven days later, he resigned from office.
December 6, 1941, a surveyor goes door-to-door with the question, "How many people in this house want to kill Japanese?" The homeowner replies, "Kill them? Hell, I don't even know where Japan IS." The next morning, the surveyor comes around again with the same question. "Hell, we ALL want to kill 'em, but grandma can't--she's in a wheelchair!"
The final stage is adoption of the new idea. Right now, we are in stage two. Libertarianism as a movement is only a few decades old. It took 60 years for communism to take hold in Europe, and another 60 for it to be rejected. We are now at the point where most people have at least heard the idea of freedom, even if they aren't sure how it works.