What are some of the references to the hour, day, month, or year? Why does Fitzgerald include so many time details in this chapter in particular?

Many of these references show Gatsby really doesn't have a good sense of time or how it works, and this symbolism is illuminated in this particular chapter because it is the chapter in which he is reunited with Daisy.  In the first paragraph, Nick says that he arrives home at "two o'clock" in the morning and was afraid that his house was on fire because Gatsby had all of his house lights "blazing."  First, it is not really appropriate to have all one's lights on at two in the morning, especially when the light would affect one's neighbors.  Moreover, when Gatsby sees Nick, he suggests that they go to Coney Island, and Nick has to remind him it is "too late."  It's as though Gatsby truly does not realize there is such a thing as "too late," and this makes sense in terms of his thinking about Daisy and their reunion as well.  He does not realize there is a possibility it could be too late for he and Daisy to be together.

Further, the fact that he almost accidentally breaks Nick's clock by knocking it off the mantle seems to symbolize his wish for time to stand still, for nothing to have changed between him and Daisy.  In the moments after Gatsby and Daisy first see each other, Nick says, "the clock took this moment to tilt dangerously at the pressure of [Gatsby's] head, whereupon he turned and caught it with trembling fingers and set it back in place."  Time does not and cannot stand still, and Gatsby catching the clock seems to emphasize this fact.

In addition, Gatsby seems bad with time now, but he knows exactly how long it has been since he last saw Daisy: "five years next November."  It's as though that was when he lost his sense of time, and he's been unable to keep track of it since then.  The fact that it was "two minutes to four" and he was panicking that Daisy wasn't going to come (when she was invited to arrive at four o'clock) confirms this. 

Thus, time is emphasized in this chapter to show us just how badly Gatsby wants time to stand still so he and Daisy can pick up right where they left off, but the fact that he catches the clock he almost breaks emphasizes that time has not stood still.  Daisy has married, become a mother, and moved on, even though Gatsby has not.  He may be able to ignore time when he is the only one affected by his choices, but he cannot force Daisy to forget what has changed since the last time they were together.