Where and when did the farce "Not Now, Darling" originate?

Hello - and thanks for your question.

"Not Now, Darling" was a great success in London at the very end of
the sixties, running there for two years before opening on Broadway in
October 1970. Read more at:

"Act One 1969-1975: Getting through by the skin of our teeth." page 21
www.oup-usa.org/sc/0195123476/0195123476_01.pdf 

Or if you don't have Adobe Acrobat Reader installed on your computer,
read it at:
"Act One 1969-1975: Getting through by the skin of our teeth." html
version
://www.google.co.uk/search?q=cache:MAzvU-ZdO4AC:www.oup-usa.org/sc/0195123476/0195123476_01.pdf+%22not+now+darling%22+london+%22first+performance%22&hl=en&ie=UTF-8

It "set box office records in London and Paris before coming to
Broadway."
https://www.dramatists.com/text/home.html

But it closed after only 21 performances at the Brooks Atkinson
Theatre.

Internet Theatre Database
http://www.theatredb.com/cgi-bin/q.pl?sid=s2324

I hope this answers your question. Please let me know if anything
needs clarification.

Regards - Leli

search used:
://www.google.co.uk/search?q=%22not+now+darling%22+london+%22first+performance%22&ie=UTF-8&oe=UTF-8&hl=en&btnG=Google+Search&meta=
and: "brooks atkinson" 1970