There are limitations on the task number functions, unfortunately, but we can still get away with using them with JavaScript to achieve this. Try out this example:
<script>
$(document).ready(function(){
if ([% CBCCurrentTask() %] <= 6) {
$('.attribute_label_column > :nth-child(2), .cbc_concept:not(.none_concept) > :nth-child(2)').hide();
}
})
</script>
There may be some analytical considerations for hiding an attribute for part of the exercise, but that is beyond my skill set to comment on.