One frequently used image of the night in A Midsummer Night's Dream is the moon. We especially see the moon referred to in the very first scene. Theseus and Hippolyta are waiting for the new moon to rise to hold their wedding day as the new moon symbolizes a new start. Theseus is pining for the moon and commenting on how slowly the moon is progressing, as we see in his lines, "O, methinks, how slow / This old moon wanes! She lingers my desires" (I.i.3-4).
The moon also appears as an image in some of the mechanicals' scenes. Not only do the mechanicals rehearse their play in the forest by moonlight, they also decide that they need an actor to play the part of moonlight in their performance before Duke Theseus. Hence, in Act 5, Starveling comes on stage holding a lantern and with a thorn-bush and a dog in tow. The lantern is supposed to represent the moon while Starveling is the man in the moon, as we in his lines:
All that I have to say is to tell you that the lanthorn is the moon; I, the man i'the moon; this thorn-bush, my thorn-bush; and this dog, my dog. (V.i.256-247)
We also see Helena refer to night imagery in her first speech in the very first scene. When her best friend Hermia greets her as "fair Helena," Helena responds by lamenting that Demetrius thinks Hermia is more fair than she is. She refers to Hermia's eyes as guiding stars, which is night imagery, as we see in her lines, "O happy fair! / Your eyes are lode-stars" (I.i.185-186).