My attempts to become un-rusty after years of doing archviz. 
Between 1-4 days for each (except Superb Man; about a week).

All models are based on the same basemesh, which means that textures, hair and blendshapes can be re-used and combined to quickly build a custom starting point for each character.
Eyes have blendshapes for iris and pupil size and the iris material can easily be randomized.

Mudbox, Maya/XGen & V-Ray. Bump/displacement maps are a mix of XYZ and hand painted.
Will be continually updated.
Superb Man!
Attempt #5
Attempt #7 - One day sculpt
Attempt #6 - Ed Harris. Still working on the likeness, textures and details.
Attempt #7 - lighting tests
Attempt #4
Attempt #3, semi-realistic study
Attempt #8 - One day sculpt
Attempt #2
Mudbox screenshot
Quick Unreal skin test. Custom made skin shader based on a few different approaches.
Old model made quickly, for fun. Released as a free model to be used in archviz.
Mudbox screenshot
Attempt #6. Ed Harris, a work in progress. About 3 days to get to this point.