In James Baldwin's "They Can't Turn Back" (1960), what does he mean by his last sentence and the phrase "time is real"?
I have edited your question as I found that the sentence you quote is in the essay called "They can't Turn Back" (1960), originally printed in Mademoiselle and collected only many years later in The Price of the Ticket (1985). The essay was one of the two (the other being "The Dangerous Road Before Martin Luther King") written during Baldwin's second trip to the South of the U.S. The author's trip occurred when the refusal to serve four black students of the Agricultural and Technical College of North carolina at a segregated lunch counter led to a vast sit-in movement throught the South.
In "They Can't Turn Back," Baldwin specifically focuses on the situation in Tallahasee, Florida, two months after balck university students had been attacked by white supremacists with no intervention from the police. Yet, the essay is not pessimistic in its main tone and this brings us to the sentence that you quote: "time is real". What Baldwin realized during the trip and illustrated in the essay is that compared to the time when he was a student, time has moved on and there has been an evolution in the students' consciousness. They are ready to fight for their rights in a way that their fathers were unprepared to do and they challenge the stereotypes and myths about African American inferiority that the previous generation had bowed their heads to, submitting, albeit unwillingly, themselves to their inferior condition. Time is real as it moves on and society changes in directions that can only take towards desegregation.