A simile is a comparison of an object with another using like or as, where a metaphor is the comparison of an object but used for describing the object.
Metaphor: I fell into a trapdoor of Depression.
Simile: I feel like a sack of potatoes.
That being said, "last night's" is neither a simile, nor a metaphor, but it is in fact an Adjectival phrase. Commonly used to describe an event.
