1967: you go too fast for me Crowley, or the year the Wolfenden report actually came into effect.
It is no secret that in 1957 the Wolfenden Committee recommended the decriminalisation of private homosexual activity between consenting adults over the age of 21, but with heavier penalties against homosexual activity in public places.
This is precisely what Anathema thinks of when she comments in the book that her book had been left in the back of the car of 'two consenting cycle repairmen'.
Not only does that inform us as readers that the characters within the book perceive Crowley and Aziraphale as being a couple, especially by the (arguably) cleverest witch in the book, but also that their appearances (physical corporations) do in fact look older than 21 years old. (the age of consent)*
*It would take until the 2000s for the age of consent to be equalised, and for lesbian, gay, bisexual and transgender personnel to be able to serve openly in the armed forces.
But coming back to the term 'consenting' and the significance within the overall plot of Good Omens series-wise is the fact that they chose 1967, precisely 10 years later after the Wolfenden report and the year the Sexual Offences Act was passed (which decriminalised private homosexual acts between men aged over 21 in England and Wales, while at the same time imposing heavier penalties on street offences) as a crucial point in storytelling.
This is the last scene we see of them after the montage; this is precisely the point where Aziraphale makes that big, first move towards Crowley and manifests himself inside of the Bentley to protect him from a burglary that could have ended in disaster. This is Aziraphale stepping outside from his own box and venturing into admitting that yes, he would enjoy Crowley's company as more than just an Arrangement. He would like the picnics, he would like to dine openly with him.
And this comes precisely at a time, a real world setting where even the Archbishop of Canterbury agreed, saying: “There is a sacred realm of privacy ... into which the law, generally speaking, must not intrude" (referring to homosexuality).
Although we know Aziraphale and Crowley are not men, but rather men-shaped beings of the world, there is something to be said about how the 1967 act reflects on Aziraphale's 'heavenly' beliefs and how that can be attributed not only to homosexuality*, but also a realm of privacy where neither Heaven or Hell (religion itself) need to interfere with his affairs.
*we do know, however, how much the book and tv series lean into Aziraphale being 'gay', at least in our human understanding of labels and categorizing even though he is not; "pansy" "nancy boys" "gayer than a treeful of monkeys on nitrous oxide" (this one specifically marking Aziraphale canonically in the book as appearing to be a homosexual) "you've got the wrong shop" among others.
A real life anecdote from the time says: John Carter was 17 at the time and doesn’t have a clear memory of the bill passing; he only realised the significance of the change with hindsight. He came out in the early 70s, after making contact with his university’s gay society, which wouldn’t have existed were it not for decriminalisation. “It meant that people could meet … and freely associate.” That was crucial, he says, because, “if you don’t even have a space where you can go, then people are cruising, they’re cottaging * ... It took many years for people who had been constantly looking over their shoulder, being worried, to develop proper ways of relating to each other. Ways that were not just based on sex or compromise or fear.”
*(No, cottaging is not living in a cottage)
No matter that the law had been passed, there was still a lot of stigma surrounding the word 'homosexual'. It wasn't until the 80s and 90s that it stopped being a crime in Scotland and Ireland; being further stigmatized with the AIDS crisis in the late 80s.
Regardless of the nature of the open confession Aziraphale lays bare to Crowley in 1967, it most definitely can be read as a 'coming out' for him. Perhaps not dealing with sexuality directly, but with religion layered on top of that. It is still too fast despite of the year, in spite of the millennia worked together under false pretenses. But it is an exterior, real life push that reinforces the idea for him to see that- if humans are able to recognize that man could be with man and not call it a crime, why could that same thinking not be applied to an angel and a demon living on Earth?
Aziraphale is doing more than blurting his heart out, he is openly hoping for the time that matches 1967 in its decriminalisation of homosexuality to one that applies for him and Crowley. So the thermos, the "better not" say thank you just yet, is a lingering promise to be there for when it finally happens. One which Crowley accepts with bare, open hands.