2dead dogs
I'm not sure where you are, but Adelaide uni have a Dr Drew Dawson who is an expert in the field.I think they have produced booklets and guidleines for extended hours rosters.
If you can produce documents by experts in the field those making the decisions may be forced to comply with a more humane shift start / finish.
To go against the advice of experts after being told is putting your head on the OH&S chopping block.
4 on 4 off is fine but the late finish is less safe and makes sleeping more difficult.