Did some searching, it comes from CIA director William Burns in 2022-03-08, you can see it here. It was actually 2 days.

"His own military's performance has been largely ineffective," Burns said of Putin. "Instead of seizing Kyiv within the first two days of the campaign, which is what his plan was premised upon, after nearly two full weeks they still have not been able to fully encircle the city."

If you go a bit further back, you have "sources" from the CIA already spouting the 2 days line a couple weeks earlier. Here's an example from the day after the start of the SMO.

US intelligence officials are concerned that Kyiv could fall under Russian control within days, according to two sources familiar with the latest intelligence.

It goes like this, US Intel are worried it could happen -> report it as Putin hinging his whole plan on it happening -> if it happens it's because it was a massive gamble and "unfair" in some way, if it doesn't happen it was an utter failure and Putin threw away his whole country.

A week later, business insider reports it as though Russia failed in the war and practically lost, and actually, it's Russian intelligence which is bad for wrongly predicting their victory. Which the US intel also predicted. Go figure.

Narrative created. Consent manufactured. Redditor fooled.

P.S.: is there a Ukrainian civil war megathread I could read and contribute to somewhere? It's fun to look up these little lies but it's been 2 years now and there's just too much stuff to hold on one's head.