The regional optouts and thunderclaps ... having seen video footage some time ago on YouTube (which I can't find now, annoyingly) of a regional gallery opting in and out of the headline sequence I can only admire the people responsible. It isn't a countdown as such, London just yells "opt out opt out" down the line after the last national headline and the timing is up to the region. It really does seem unnecessarily complicated and it's amazing we don't get more crashes and untidy mixes.
London doesn't usually yell...
Most directors I've heard are perfectly calm and just call the opt in the same way as presentation do, with a clear 'opt-out, opt-out'. They trigger a timer that counts to the opt-back with a digitised voice which is sent to the regions along with the director's talkback (the digital voice used to be Fiona Bruce, not sure if it is now Sophie Raworth). When that timer hits zero they call 'opt-in, opt-in' (some may say 'opt-back, opt-back')
UKnews and deejay gave kudos