This post made me wonder at what kind of rate the bombers were being built so did some searching and found this about one plant:
“Willow Run, also known as Air Force Plant 31, was a manufacturing complex in Michigan, United States.
It was thought to be the largest factory under one roof anywhere in the world.[11] The Willow Run plant featured a large turntable two-thirds of the way along the assembly line, allowing the B-24 production line to make a 90° turn before continuing to final assembly.
Ford was rolling a Liberator off the Willow Run production line every 63 minutes, 24 hours a day, 7 days a week.
At its peak monthly production (August 1944), Willow Run produced 428 B-24s with highest production listed as 100 completed Bombers flying away from Willow Run between April 24 and April 26, 1944. By 1945, Ford produced 70% of the B-24s in two 9-hour shifts. Ford built 6,972 of the 18,482 total B-24s and produced kits for 1,893 more to be assembled by the other manufacturers. The B-24 holds the distinction of being the most produced heavy bomber in history.”
A small part of the world's largest one-story war production plant, the giant bomber factory at Willow Run, Michigan. Fixtures in background hold bomber wings during assembly, 1942.
en.wikipedia.org