It’s important to note that movement does NOT happen on a numbered count. Think about it. If you are walking and count each step as your foot hits the floor and freeze on the count, you are not moving [at that moment]! If you clap your hands to a beat, each time that your hands are together (on a numbered count), they are not moving. In relation to counting along with beats of music or a regular rhythm, ALL movement occurs between the counts. Note, too, that movement is not just steps (in any direction), it is also turns.
Therefore, the correct way to count when to execute a one-footed turn is not “step-turn,” which would require taking a step and then turning on the count, but “turn-step,” so that you are turning/MOVING between the counts and then “hitting” the step on the numbered count.