We called the dog watch the evening 4 to 8. It was split in the navy to the 1st dog watch and second for meals.
The thing I remember about the 12 to 4 was in my time your social group was confined to the third engineer and a junior and on a tanker where you never broke watches that was it for months at a time. On modern ships with UMS the second mate must lead a fairly solitary existence. Especially when they are likely to have little in common with the crew.