Hi Andras - that type of shape is going to be pretty difficult to model in only 20 minutes in any kind of software I think...

But probably one of the displacement brush stroke based modeling programs like ZBrush mentioned above would be the fastest I would think.

If you've tried ZBrush before and did not like it, then also give 3D Coat, Sculptris, and Blender sculpt mode a try and see if any of those are more comfortable for you.

- Michael