These are all correct, but are very formal. I would change them to read:
A: I left work an hour ago
B: Really? How long did you work today? Did you have lunch today?
A: For eight hours! I didn't, but I did eat an apple.
B: You must have been hungry after eight hours! (since you're already discussing the fact that person A worked, you don't really need to bring it up again. You can, and both ways you used work fine, they're just a little more formal than most casual conversations would be.)