About five years, for Finland's critical thinking curriculum. (First results, to latest.)
However, that requires an education system that can be easily updated, and widely rolled out, without being shotgunned by anyone who has already lost their critical thinking ability, who may be in a position in government.
Yeah, i'd imagine one cycle of high school oughtta get everyone through at least one class, with the new life experience to have actually used and explored it. Teach it in homeroom where you teach the other mostly bs but sometimes valuable things, make em do 2-3 weeks on it and for gods sake have the curriculum written by experts and NOT BY POLITICIANS. I can't think of anything worse than a "bipartisan effort to design curriculum though congressional committee"
However, that requires an education system that can be easily updated, and widely rolled out, without being shotgunned by anyone who has already lost their critical thinking ability, who may be in a position in government.