10 - 15 minutes
My daughter dropped the phone in the toilet early in it's life. It was retrieved quickly and dried with the rice technique, but it never has been able to fully charge and would frequently go from 30-20% to nothing very quickly.
Quick! I thought it might be a challenge, but everything was smooth. We didn't bother with removing the entire screen, we just held it out of the way while the other removed screws and battery.
I should have done this a year ago.
You may need to fully remove the screen if you're working alone, but we gave it a try while leaving it attached.