1 - 3 horas
After many drops, the display on my iphone 4 finally broke. A new iphone 4 is around $600 outside of upgrade time so I figured I'd try a repair.
It took a bit less then 2 hours to perform the repair with the provided guide. I have clumsy gorilla hands so more nimble folks may have an easier time. The guide was good functionally, but the screw sizes they mention seemed to be different then what is in my phone.
Line up the screws and small bits by step number since the sizes mentioned may be different from your phone. Use a well lighted work space. A rubber work-mat helps a lot so parts don't slide around. I have bad eyes so a magnifier was helpful.