I’ve thought Newfoundland should be on the hour:
52.5 - 67.5: Atlantic
67.5 - 82.5: Eastern
82.5 - 97.5: Central
97.5 - 112.5: Mountain
112.5 - 127.5: Pacific
The Michigan mitten and Tennessee would shift to Central time...
Amazing the lack of consensus here, or maybe not, considering stepping one foot to the west on any of those boundaries changes you ST to DST