Related to the OP and neonatology....
I wouldn't really consider neonatology to be a job that works the "least hours." When on the clinical service, I work 60-80 hours a week and so do the vast majority of my colleagues. I know enough other groups to know this is not atypical and certainly 50-60 hours/week is common. I take in-house night call and most neonatologists who are not near retirement take either in-house or home call. Increasingly, it is in-house call in the larger NICUs. A lifetime of taking in-house call would never be my idea of a "least hours" type of job.😉
There are shift jobs, part-time jobs, and night-float attending jobs available and these are certainly appealing for some people, especially when they have other commitments, such as working for the FDA (one person I know...).
Over the long haul however, the majority of neonatologists will primarily not be doing it as a shift job either via being a night float doc or doing only 24 hour shifts. The benefits, both to doctor and patient, of continuity of care make neo very different than EM. Even those doing it as shift work will be almost always be doing quite a few nights.