One big rule that we never ever break is to open a can of ale before beer o'clock. Luckily this can be anytime betwen 1000 and 1300 hours and woe-betide anyone on watch who forgets to waken the other at this crucial time of day.
2013, Dave Lewis, chapter 62, in Raising Skinny Elephants, [Pontypridd, Rhondda Cynon Taf, Wales?]: Ponty Press, ISBN978-1-291-37289-2, page 231:
When Hal woke up he decided it was beer o'clock and had the girls' permission to wander down the road for a few pints before tea.