Late Embryogenesis - Carnegie Stages 17-23
The skeletal 'scaffold' is place by Stage 23 (last stage in the development of the embryo).  During this time frame, the unwinding of the leg clearly visualized. 
(1) From Stage 17 to 18 the plantar surface of the foot rotates from a caudal to a sagittal plane position (soles facing one another).
(2) From Stages 18 to 23 the legs are unwinding.  The posterior compartment of the lower limb rotates from a caudal (facing upwards) to its neonatal position.  This leaves the foot in supinatus at the end of Stage 23.
Fetal Development
At approximately week 10 post ovulation, the heel and lateral column of the foot begin to unwind toward their plantargrade position. Between weeks 10 and 11 po, the talar head and medial column of the foot begin to unwind toward their plantargrade position. 
Carnegie Stages Adapted and Revised, courtesy of the Carnegie Human Embryo Collection
Animated Model of Embryogenesis - from when the lower limb bud first emerges to the end of the embryo stage of development.  This is an excellent view of the torsional developments that occur within the leg during the first trimester of life.