According to the Booklet of the first Kimetsu no Yaiba: Hashira Training Arc Blu-ray, here are some info about the First episode:
-First episode Storyboard draft was sent/uploaded on April 16, 2022
-Dubbing/recording session: June 2, 2022
-Storyboard Draft completed on September 17, 2022
-LO work started around October 18, 2022
-1st episode aired on May 12, 2024
S4 was being worked shortly after s2 was finished airing. In a time where exploitation of employees has become more or less a norm, rushing projects, finishing eps just a day before airing or even delaying ep releases mid season it's good to see studios like Ufotable or KyoAni still maintain a healthy scheduling for high quality productions with mostly just with in-house workforce.
by No_Name0_0