This depends largely on the model in question,.. it's size,.. how much detail is in it,.. etc,..
But for an average human-esque model,.. I average about 4 hrs start to finish. But my results are terrible. Many others spend far more time painting, and/or spend lots of time between coats letting things dry completely,.. leading to days/weeks on a single figure. And a lot of it will depend on how many techniques you employ,.. how many layers/shades you are doing, as well as what quality results you want to achieve. What are you looking for? Table top Quality?,.. Showcase Quality??,.. Golden Demon Winner??