While the Peary was built in 4 days as a publicity stunt, by 1943, the US was building Liberty ships in about a month (depending on the exact shipyard) from keel to launch.
It should be noted that one of the surviving Liberty ships today, the SS John W Brown, was the third Liberty ship launch of its day... at Baltimore alone, not counting the other shipyards also producing Liberty ships. Which should give you an idea of the sheer scale of Liberty ship production (it's the largest ship class ever built).
It wasn’t true (in the sense of a sustainable rate), but it makes for good appearances and propaganda.
https://en.m.wikipedia.org/wiki/SS_Robert_E._Peary