#4 - Happy Hour. Certainly happened in 1966 at the RAF College of Air Warfare, Manby. A very mixed and sociable Mess population. As a watch-keeping ATCO, my attendance was however variable! Uniform not worn after 1900, IIRC.
Never heard of an All-Ranks edition as mentioned at Post #6, but then there would always have been local variations on the theme.
At Tengah in the late 60s HH finished promptly at 1900, when one was required to change rig into long sleeves and trousers.
In the early 70s at Eastern Radar, RAF Watton, it ran from 1700 until ENDEX, with food c. 1900 to benefit the watch-keepers coming off-shift at 1800. House rule was “No WAGs before 2100, and thereafter at their own discretion!” Uniform was regularly worn in the Bar, as controllers came and went all the time (it was a 24-hour Unit).