Will you now have three hours?

Question

Two persons A and B have known each other for a while. A is interested in B's life. One day, A gets up the courage to ask B a question.

A: Can you tell me about your life?

B: You got three hours?

A: Yes, I do.

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I can't change the boldfaced sentence to the following:

B: Will you have three hours?

This is wrong.

But if I add the word "now"? Does it work?

B: Will you now have three hours?

A: Yes.

Answer 1

Will you have three hours?

is not wrong, it just needs a context set up in the future. For example,

When you are done with this... Whenever that will be... Will you have 3 hours for me [then]?

Adding now to this sentence makes it semantically incorrect. You simply can't use now in the future.

-I am fixing my car.
-How much time do you need?
-20 minutes.
-Will you have 3 hours now? (it doesn't make sense)
-Will you have 3 hours then?

However, you can use now if the context is set up at the present time.

We will now rise and sing the National Anthem. (from your comment)
And now I will perform a magic trick!

In stories and accounts of past events, now is used to refer to the particular time that is being written or spoken about.