Doing baby mills and regular windmills are two totally different techniques, You should learn your headmills/popping mills first.. Unlike windmills.. babymills require you to use your waist and your upperbody to keep the momentum going... Its like a kip up while you roll on your upperback... I posted a clip showing you exactly how to babymill in the windmill section.. you should check it out... much love bro
Timewise... after learning my headmills/popping.. it took me about a good week...
Post if you have any other questions dude
http://www.bboy.org/t50861/s.html