In hospitals nursing shifts go:
7am-3pm
3pm-11pm
11pm-7am
I wanna know why? My theory: 3pm: people getting ready for dinner, 11pm: people readying for bed, 7am: people getting up, ready for brakfast.
These days 8 hour shifts are more the exception than the rule. The 12 hour shift has become very popular among hospitals and healthcare workers alike. More days off for the nurse and fewer full time positions to fill for the hospital, not to mention that continuity of care is greatly improved.
At my institution, most shifts start at 6:30 and 18:30. Breakfast is served around 8:00, allowing time for early morning testing to be done before the patients eat. Dinner is served around 17:00. This eliminates the need for extra staff to be on to shuffle meal trays, feed invalids etc. during the p.m. shift. This would also work with the 8 hour shifts the OP described.
To extend the question a bit, why are the three 8 hours shifts broken up like that? Why not have at least one of them a ‘normal’ nine-to-five?
I work for a large junk mail and product sample packaging company, and they have these same shifts. As does the steel building manufacturer next door to them.