In port and approaches etc. should be hoisted at sunrise and down at sunset. Now these times are dictated by astronomical phenomena ... but generally ignored.
At sea it is only if 'challenged' by others such as naval vessel etc. and not necessary to 'fly'.
The background to 'dipping to naval force vessels' apparently stems from the old Brittania rules the waves days - when we blew shit out of anything that didn't recognise our 'authority'!!
It spread to ther navies, as we lost control of the oceans etc. In fact it is no longer required by any naval vessel for us to dip to them. but shows a voluntary mark of respect !! In my latter years at sea on merchant ships - it was not uncommon to see an AB / Middie run along the deck to dip when they got caught out by us !! That is if they bothered at all !!!!!!! I actually had a VHF call after dipping to one vessel ..... he didn't dip, but apologised that he didn't see it very often now and didn't expect it to be done.......
In harbour; Winter 9am 'til sunset Summer 8am 'til 9pm or sunset whichever is sooner.
Should be shown in all teritorial waters at all times except when racing. On the high seas when in company and when entering or leaving port.
For all of you who got it right give yourself 10 housepoints for all of you that got it wrong give yourself 10 flogs of Paulineb's whip! (See her picture for reference!)