Let’s test it out. If you are genuinely interested in an answer to “where did the idea of a 3-day special military operation come from?”, here are some facts and sources. I suspect you put those qualifiers in there so you can dismiss them but let’s find out.

There’s a few along those lines.

• 3 days, and official: a report of victory from state-run media about the conquest of Ukraine, released on 26 feb 2022 (and then quickly removed): https://www.newsweek.com/state-run-russian-news-site-accidentally-declares-ukraines-defeat-1683455
• not Russia but Russian ally Lukashenko: https://x.com/nexta_tv/status/1498185064617762816
• not 3 days but a massive underestimate from Putin: https://time.com/3259699/putin-boast-kiev-2-weeks/