My friend just took 400mg of temazepam, she's at the hospital now. how long would it take her to wake up? :-(

Not clear: Your friend is lucky that she made it to a hospital. They may be able to give her a medicine that reverses temazepam, and helps her wake up. But most overdoses involve more than one pill or alcohol, and that complicates things. You can hope that she has no lasting injury, but it isn't clear. And insist that she get treatment for psychological problem. IF you believe in prayer, then by all means.