Some more - published - sources for "not before long":
John Fobanjong (Prof., UMass), Understanding the Backlash Against Affirmative Action
Not before long, however, affirmative action's "golden age" would gradually come to an end with the retirement of Justice Warren in 1969 and the appointment of Justice Burger as the new Chief Justice of the U.S. Supreme Court.
Laurel Brake (Prof. Emerita, Birkbeck College, University of London), The Endings of Epochs
Not before long was Decadence condemned in nearly every quarter of the literary establishment.
Aviva Drescher, Leggy Blonde: A Memoir
Her facade would crack, though, and not before long. “When you came out of my womb, the first thing I saw were your long, long legs,” she used to say when telling the story of my birth.