When does one become liable for wearing Sha'atnez? Is it merely putting the garment on one's body? Is it when the act of dressing is complete (ie., buttoning the last button, zipping up the zipper, etc.)? Or is there some measurement of time or distance walked while wearing the garment that effects the violation of the prohibition?
It seems clear (as I have been taught too) that liability begins as soon as one gets benefit from the garment.