The story
First use appears c. 1942, US, advertising copy written by Jules B. Singer of the Federal Advertising Agency for the Gem brand of safety razors, made by the American Safety Razor Company.
Etymology from Wiktionary, CC BY-SA 4.0.
five o'clock shadow
Today it means: A dark appearance on a man's chin and face caused by the slight growth of beard that has occurred since he shaved in the morning. Full definition →