SAR - I am not sure if you believe this idea of some in depth secret paper showing the benefit of night HEMS, but I am afraid it is just rubbish. There is no published data on the benefits of night flights. Period. The ambulance service may be able to meet their targets with less ground resources but there is no evidence of benefit. If there were any, it would be published as a peer reviewed paper in the medical literature.
And sadly I strongly suspect based on the last 27 years that there wont be any such paper in the future. If only because a proper audit would shut me up!