I dropped my Kindle Fire and its glass touchscreen got cracked. The actual LCD worked fine, as did the touch functionality, but the crack was very visible.
The repair went almost flawlessly. I don't know how long it took, as I tend to lose track of time when fixing electronics. The guide I followed, which for some reason IFixIt is not letting me select as a "relevant guide" for this review, was Phillip Takahashi's "Installing Kindle Fire Front Glass Panel": Kindle Fire Front Glass Panel Replacement
The screws in the Kindle Fire are absolutely tiny. Keep them in a box so you don't lose them.