Flash Comics #1, featuring the first appearance of the Golden-Age Flash character hit newstands on Nov 20th, 1939.
75 years and four days ago.
Which is why DC Comics are running a series of 75th Anniversary Flash Variant covers and other promotional material in January 2015.
The year of his 76th birthday.
Bleeding Cool's Mark Seifert tells me "The usual explanations apply. Yes, it has a Jan 1940 cover date, that's when any remaining copies were to be removed from the stands. Different places around the country would have had it on the stands on varying days or even weeks. Nov 20 is the canonical on-sale date, IMO, based on copyright records. There is a DC house ad from the prior month that stated Flash Comics 1 would hit "about Nov 10", but again, if you're going to pick a date, I'd take Nov 20 to be the date to pick."
So, basically, not January.