There was both a Black Thursday and a Black Monday, 1929. Black Monday came the week after Black Thursday. I thought Black Monday sounded better than Thursday, but "Before Black Thursday" would also work well.
There was also Black Monday, 1987, which was the worst stock drop since Black Monday, 1929.
ooh I like some of those like speak easy or what about black before monday instead of before black monday. I know it makes no sense in context at all but thats how I originally read it and I quite like. I like the idea of going with a 1920's theme.