Time is an important component of If Beale Street Could Talk in several ways. Because Fonny (Alonzo) is incarcerated, and Tish and his other advocates are trying to get him released, time is relevant to the length of his jail sentence, including the ways that both of them endure it. Early in the novel, the reader learns that Tish is pregnant with their baby, so time is closely connected to the length of her pregnancy.
Both of these aspects are reflected in a line of dialogue that Tish speaks while visiting Fonny in jail, when she lets him know that she is expecting.
I'll work up till just about the last month. ... And anyway we have you out of here before then.
Tish, after leaving the jail, thinks about how the time will pass as she works toward and waits for his release.
[Y]ou just have to somehow fix your mind to get from one day to the next. If you think too far ahead, if you even try to think too far ahead, you'll never make it.
While she is riding the bus home, she worries about their predicament and wonders if she will feel these anxieties forever.
You ... wonder if you're going to spend the rest of your life going back and forth on this bus.
Tish also thinks about time as she reminisces about getting to be friends with Fonny when they were children growing up in the same neighborhood, long before they became a couple. She associates different streets in the neighborhood with different days as each has its own mood. Walking down one street, she observes
It was the Sunday morning street. Our streets have days, and even hours.