Today I repaired an iPhone 4 that was in working condition but had broken front and rear glass. 
It took about 2 hours, longer than the estimated time. I suppose it would take less time for someone more tech savvy than myself, and/or someone who had done it a few times.
Given the nature of my work at iFixit, I thought I would have done this a few more times than this. Ne’ertheless, I shall continue on, and will hopefully do more of this kind of thing. I really had fun!