" One more most important thing is exactly at what time does the heel of the standing foot starts to leave the floor. Where is the moving foot at this time."
For a rising step, the worlds leading coaches teach that the heel MUST break from the floor slightly BEFORE the other foot passes.
For a non-rising step they teach that the heel rises only after the foot has passed, because they stay in a relatively lowered position when they do this.
Many people initially believe this contradicts the text books, but in fact it does not - the text books illustrate the actions of a walking exercise executed at standing height, not the action of any real dance step which will either be executed with a rising action, a falling action, or at a lower height than this exercise. Real dance steps are all modifications from that starting point, with different details.