For 9 years, George Brenner produced The Clock, starting in 1936 and ending in 1944. In the beginning, The Clock appeared in the Comics Magazine Company's "Funny Pages" from November 1936 until June 1937. The Clock made additional appearances in CMC's "Funny Picture Stories # 1" and "Detective Picture Stories" numbers 1 & 5, with reprints appearing in the first two issues of "Keen Detective Stories" (July & September 1938).
In December 1937, The Clock began appearing in Quality Comics' "Feature Funnies" (eventually called "Feature Comics") from issue 3 through issue 31. The character was then published within the pages of "Crack Comics" for the first 35 issues, ending in "Fall" 1944.
From reading different articles and whatnot in magazines and on online, it would appear as if Brenner simply claimed ownership of The Clock when he went from working at the Comics Magazine Company to working for Quality Comics.
Even though The Clock saw his last new story produced before the end of World War II, his nine-year run is comparable to such popular characters as The Black Terror, The Shield, Quality's Midnight & The Target, and longer than the runs of the Golden Age Cat-Man, Green Lama or Black Hood.