40 minutes - 1 hour
I attempted to replace a depleted battery and ripped the LCD ribbon cable popping the front off my iPhone 5 (should have bough an iSclack). So I needed to get a complete replacement display assembly to get my phone back.
The nice thing about fitting a new screen is that you don't have to remove it from the phone first, so you avoid the risk of damaging the ribbon cables. Moving the extra bits from old to new screen was mostly easy, although unsticking the button contacts was a bit tricky. Reassembly was smooth (including the new battery), and everything was perfect on power-up.
Other than getting off the old display without damaging the LCD ribbon cable (which doesn't matter if you're replacing the assembly), this is surprisingly doable. I see so many people going around with shattered screens, there's no need!