Cue Dots were also "flashed" by NC1/2 ahead of live programmes, as part of the line up. They'd be on the phone to the production gallery, confirming on air time, duration etc and would put on the cue dots temporarily to check they could see them. All studio centres and OBs therefore needed an off air monitor. There were occasions where Cue Dots couldn't be seen during line up, if a region was opted out for example. This was a good way of checking.
BBC Cue Dots (as has been discussed before many times) were used by network control to cue a live programme, not the other way around. If memory serves, they went on at 1'00 to air, off at 10", back on again at 5" then off at Zero.
When digital distribution and digital television became the norm, the BBC ceased use of Cue Dots, as the delays inherent in the tx system meant they were no longer near-instantaneous.
Two minutes regions...