Anthony Fauci, the entire CDC, and even the White House presented that as an initial timeline. When "the lockdowns" started that was the official position. After they were in place it quickly slipped to three weeks, then we don't know, then "long enough to flatten the curve" or maybe "until everyone gets a booster."
> specifically which experts
Let's not devolve to senseless parsimony over this topic again. All of this is well documented and if you actually wanted to know you could have easily found it yourself.