My guess is after 1983. The shot of the card with Brian on it when John talks of Raincloud Productions... I had those cards when they originally came out in '79. I still have a few including that one. The other hint that it may be from 83 or in the vicinity is when he spoke of buying a house in America. This had to be in California for when they would eventually begin studio work for The Works sessions. It's interesting to note that he spoke of his Victorian house and that his kids go to a Catholic school. I've never heard him reveal any kind of information like that before even if it was in such short detail.
I think it's from 1983. John bought the house in LA around 1982 (which is what he meant by 'last year') and it was in fact a holiday house as he spent Easter 1983 there with his family.