Joan left home the night after her Friday radio show, coincidentally the same day that Bill suggested she mysteriously disappear for a publicity boost. The next morning, Mr. Crandall tells Lt. Hackett that Bill floated his publicity idea "the day before yesterday" which would have been Thursday, not Friday.
It is established story is happening in 1940 and that Joan's radio program airs on Friday evenings, but the very famous 1940 Seabiscuit horse race that is announced in a "news flash" five minutes after the end of one of Joan's shows happened on a Saturday. Also, the news flash was heard around 5:30 p.m. in New York when the race in California had a post time of 4:26 p.m. Pacific Time, which would have been 7:26 p.m. in New York.