Manager: We (meaning you) need to do task A. How long will it take?

Me: Task A will take X days to do.

Manager: That seems awful long.

Me: How long do you think it should take?

Manager: It surely could not take any longer than Y days.

Me: Ok, it seems you have an answer to your question then.

Later:

Manager: It’s been Y days, why isn’t task A done yet?