I would say it's from the time Doro was filming the documentary with Queen during the Magic tour in 1986.
By the way, this was very refreshing to see. I love John Deacon.
I agree with both Rick & Mr. QueenFan, this interview was shot by the Doro crew for the "Magic Years" 3 parts-documentary released in the Uk on November the 30th 1987 (link. It certainly was shot after the Magic Tour and prior of that release date so late 1986-early 1987 is the correct answer ;)
I think John's ending comments are a bit disingenuous. I DON'T suppose he knew Freddie was ill at that point - whether 1986 or 1987. But it is rumoured he wanted out in that timeframe. So I suppose his take might be "wait and see if things get better and if they don't then I'm off". Pure speculation, of course. :-)