In September 2021 the plans for the Queen's death were leaked https://www.politico.eu/article/queen-elizabeth-death-plan-britain-operation-london-bridge/
Read some key quotes from the article.
"The U.K. government website β GOV.UK β will display a black banner at the top. All government departmental social media pages will also show a black banner and change their profile pictures to their departmental crest. Non-urgent content must not be published. Retweets are explicitly banned unless cleared by the central government head of communications.
The royal family will announce plans for the queenβs funeral, which is expected to be held 10 days following her death."
10 KNOWN upcoming days of "darkness"
"Internally, the day will be referred to as βD-Day.β Each following day leading up to the funeral will be referred to as βD+1,β βD+2β and so on."
Could this be what D5 refers to?
Other D5 meanings include: An avalanche, December 5th...
This realization I had was what finally prompted me to make an account and stop lurking.
Interesting that they were leaked a year ahead of time!