No, the notion of Ukraine falling in three days did not come from Milley. It was a common sentiment in Russia at the time and nowadays it's considered a massive intelligence failure that is openly spoken about.

Vladimir Chirkin, the commander of Russian ground forces 2012-2013:

  "Everyone, if you recall, started saying in February 2022 that the war would be over in three days. We'll beat them all now," said Chirkin in an interview on November 27 with Russian radio outlet RBC. "But unfortunately, it didn't work out that way. I would give our entire Russian intelligence community a failing grade," he added.

  In the RBC interview, Chirkin said that Moscow had "traditionally" miscalculated the balance of power, underestimating its enemy and overestimating the performance of its own forces. Chirkin said that Russian leadership had been misled into thinking that 70% of Ukraine's population supported a pro-Russian government. "It turned out to be exactly the opposite. 30% for us and 70% against," he said. "During the first few weeks, we were taught a seriously cruel lesson."