40 minutes - 2 hours
Audio quality from the earpiece speaker was terrible.
Used the repair guides at Ifixit.com the speaker replacement went perfectly.
Only to find out the issue was likely caused by 4? Years of pocket lint, earwax and goo buildup in the speaker grille.
Replace the speaker.
It's cheap and sounds GREAT.
But also take the time to clean the speaker grille.
You should be able to shine a light though that grille (speaker removed) and see light I saw.... A potato.
It was pretty bad