Here's what we know about them:
* Origin: The Muses were the daughters of Zeus, the king of the gods, and Mnemosyne, the goddess of memory.
* Number: There were nine Muses, each associated with a specific art or science.
* No Birthdate: As mythical beings, they don't have specific birthdates. Their existence is tied to the Greek pantheon and the stories about them.
In essence, the Muses are a concept rather than individuals with a concrete timeline. Their "birth" lies within the realm of mythology and storytelling.