Answer: Hi! This would be the correct way to write the sentence: It's time to eat, Aunt Nora.
Explanation: If you wrote your sentence like this (It's time to eat Aunt Nora.), you'd be implying that you want to eat Aunt Nora.
Hopefully, your assignment doesn't want you to write it like that... eating your aunts, uncles, and auncles isn't a good idea, in my honest opinion... /joking
As you could likely tell, placing the comma (also called the Oxford comma) before the person being addressed is very important in literature!
Hopefully, this helps you out. Have a good day! :)