https://www.bicycling.com/news/a46129587/lance-armstrong-reveals-how-he-cheated-doping-drug-tests/
“You could smoke that joint and go to work driving your tractor (and) in two weeks test positive, because the half-life is much longer,” Armstrong told Maher. “With EPO, which was the rocket fuel that changed not just our sport but every endurance sport, you have a four-hour half-life, so it leaves the body very quickly. With a four-hour half-life, you can just do the math.”
By “the math,” it can be assumed the Armstrong was referencing the length of an average Grand Tour stage, meaning, by the time a stage was finished and Armstrong might be tested, the level of EPO in his system was undetectable.