How long does it take most hard of hearing people to learn to read lips?

Question:

I have several hard of hearing friends but I haven't been in contact with them. All of them can read lips very well. One even fooled me, she's completly deaf now, but I didn't even know she was deaf because she could read my lips so well! (and to think, I was trying to tell her how to pronounce things in japanese x_x oops)
Any way.
If someone is hard of hearing from a young age (2-3) and grows up that way how long does it normally take to learn to read lips if they practice very hard?

Thank you.

Answers:
Some people have the ability more than others. See, i'm not deaf, but I have learned American Sign Language, and when you take the class, they tell you that you have to be able to read lips and body language, which is not an easy task, at least not to me. Just some people are born to read lips, whether you are deaf or hearing. [or hard of hearing] And hey, don't feel bad about telling her to pronounce things in japanese, you had no clue. [: But yeah i'm not sure if you can practice to read lips.

How long does it take most hard of hearing people to learn to read lips?

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