"Luckily the clock took this moment to tilt dangerously at the pressure of his head, whereupon he turned and caught it with trembling fingers" - Symbolic. Gatsby is trying to control and manipulate time by aiming to repeat the past, it's uncontrollability is evident here, as he only holds a "trembling" grasp, much like the "trembling" grasp he reaches out for in chapter 1 when he aims to captivate the green light on the dock. Even with Daisy, he has not quite yet fulfilled his desires. Time is against him.