Can First Line Supervisors have a start time of 9 to 9 and employees have start times of 7 to 7. This would give continuity of supervision who would know where jobs are at, priorities and such and allow the previous shift supervisor to kick off the next shift with better results. Would there be any legal implications applying this practice.

There is no reason whatsoever why you should not have overlapping start times. There is not even a whisper of a legal requirement (in any state) that all employee start at the same time.