On my fictional planet humanoid aliens have evolved on one continent, and have since spread around the entire planet, just like humans did on Earth. On Earth humans have since developed slightly different physical attributes, such as skin color, nose size, ear size etc; therefore for the sake of realism I too want this to happen on my planet as well.
But my question is now: How long would a large sustainable group of my humanoid aliens need to live separately from any other group before they developed a notably different appearance than that of another group of humanoids -- provided that they were identical to start with.
Based on these assumptions:
My planet is compatible to Earth, i.e., the same distance from the sun, same temperature, same gravity and same variations in temperature, radiation and other things which may influence the rate of which my humanoids change. Furthermore all the biomes and ecosystems of Earth are present (more or less). I am however both interested in how fast these physical attributes would develop in similar and different biomes.
The humanoid aliens look, behave and reproduce just like humans -- for the sake of simplicity.
With separate I don't mean complete isolation; the different groups may still trade with one another, and there may still be some genetic exchange along the trade routes; I simply mean that the majority of the population -- who presumably live as farmers or fishers -- are never brought into contact with other population groups. (The separation may also be separation by time, since I intend to follow the development of this society through at least ten millennia)
Since I intend to use this world in a computer game (which mostly should be first person) a notably different appearance therefore is one that the player can easily notice even from quite a distance, like for instance a different skin color, or a 2 centimeters different nose size. Therefore -- and because each set of physical attributes will require me to save some data -- I consider any height difference of less than 5 cm, a face feature location difference less than 1 cm or a skin or hair color hue, saturation or brightness difference of less than 0.1 (if all goes from 0 to 1) to not be a notable difference (because it will be within range of the automatically generated random variations).
(BTW) I am interested in how quickly the physical attributes will change, not how they will change
(as response to a comment: in this specific case i care only about genetical physical attributes, not man-made physical differences, such as clothes, tatoos, or any other attempt by my humanoids to alter their appearance)