A 1941 issue of the Catalina Islander Newspaper lists Hank the Night-Watchman as airing 10:00 PM to 6:00 AM on KFVD-AM. According to Billboard, starting in 1943 Hank also had a 1-hour Sunday slot on 1020 KFVD-AM. It ran 3:30 PM to 4:30 PM. But the program was sponsored by the Victor Clothing Company and he was named at the bottom of many of their newspaper ads in the California Eagle Newspaper as early as 1941. But radio logs put him on starting at Midnight on 1230 KGFJ-AM, up to 8 hours a night, 7 days a week at least as early as 1942.
The book Swingin' On The Ether Waves by Henry T. Sampson mentions the program in the same breath as Al Jarvis. It's an important benchmark. Jarvis was on KFWB from 1932 to 1960. He owned the night. The book Long Tall Dexter by Stan Britt claims that Hank was preceded by Jack the Bellboy. There wasn't exactly a baton pass.
Jack the Bellboy was running 11:00 PM to 4:00 AM on KFVD prior to 1940. He may or may not have any connection to the "Jack the Bellboy" name being used on WJBK in Detroit starting in the late 1950s. (At WJBK several DJs used the name including the legendary Tom Clay. In terms of there being a big overnight rhythm & blues show in LA, Hank succeeded Jack, but their tenures overlapped from about 1937 to 1940 and Al Jarvis lapped them both. They were all flipping hot jazz records.
In 1941 KFVD moved from 1000 to 1020 kHz. After 1943 Hank gets scarce. The popularity of the program led to copycats. Sweet Dick Whittington as playing the part of the Night Watchman on 960 KROW-AM overnights. In 1943 Billboard reports that Bob Anderson at RKO signed Blazak for a multi-year deal, and the press on him dries up right after that.