The often quoted number of a B-24 an hour is mainly war time propaganda. Charles Sorensen, a VP at Ford and Director of Production, came up with the idea. In 1942 less than 100 B-24s came off the assembly line at YIP. Ship #1 took 8 months. The factory did make a bunch of "knock down" sets of parts for other factories in the US. In 1943 1272 B-24s were completed at YIP. In April of 1944 with most of the production bugs worked out, the production schedule was increased to 455 planes in 450 hours, a plane every 59 and a half minutes (25 working days x 2 nine hour shifts) as a
PR stunt. For most of 1944 the goal was 275 planes a month which was raised to 308 for the month of November. Production ended on 28 June 1945.
All data from the book "Willow Run" by Warren Kidder quoting plant records.