2 - 5 minutos
iFixIt have a Black friday sale, I got an impulse buy. :)
Badly... At first I managed to lose one Philips screw. So, my iPhone now has 1 Pentalobe screw which can't sit tightly in their hole - that one sticks out 1-2 mm. Second Philips screw was bolted good. :)
Don't do things in 3 AM while you nurse your 2 month old baby to sleep, already tired :) And play with small screws on small tables, use biggest table and much light when possible.