Against the Day

[jbor at bigpond.com]

> the book is called "Against the Day"

"In 1955, at a meeting of the Southern Historical Association in  
Memphis, Tenn., the novelist William Faulkner shared the platform with  
a group of black and white educators. His very presence was a daring  
act of defiance at a time when whites across the region were rallying  
to the defense of racial segregation and the White Citizens  
Councils—Klansmen in business suits— ruled his home state. This was not  
an easy choice for Faulkner. While he was a Nobel Prize winner in  
literature, he lived in Oxford, Miss. Most of his friends and neighbors  
believed that segregation was right and just and moral. If he was  
emmeshed in a quarrel with his region, it was a lover's quarrel for he  
was Southern to the core.

But when it came his turn to speak, he did not mince words. Whatever  
the difficulties of ending segregation, he said, it was essential to  
recognize the core of segregation's inhumanity. Those who loved the  
South had a special obligation to "speak now against the day, when our  
Southern people who will resist to the last these inevitable changes…  
say, "Why didn't someone tell us this before? Tell us this in time."

In the end—whether optimistic or pessimistic —our obligation as  
scholars, as citizens, as human beings, remains unchanged. We must  
speak now—and act—against the day when a future generation asks: "Why  
didn't someone tell us this before? Tell us this in time." [...]

http://www.publiceye.org/magazine/v19n3/carter_wallace.html

http://www.olemiss.edu/news/dm/archives/97/9709/970926/ 
970926N2brademas.HTML

A quick google shows the phrase also to have Biblical provenance  
(usually re. "the Day of Judgement"):
E.g.
Job 38.23
Proverbs 21.31
2 Peter 3.7
Romans 2.5

best