Jesus' Activity in the Gospels: "only some three weeks"?

There is an idea attributed to B. H. Streeter (1874-1937) that attempts to articulate how much time Jesus' narrated ministry, in the canonical gospels, actually takes up. He is reported to have said that the action described in the gospels, with the exception of the Temptation story, would actually only occupy about three weeks. The point he is apparently making is a good if rather obvious one -- that what is narrated about Jesus' life in the Synoptics and John, even if it is were all historical, amounts to the tiniest fraction of Jesus' life. 

But did Streeter actually say this, and if so, when and where? I have been searching for the origins of the idea, and the earliest reference I can find is the following:

"They [the gospels] are extremely brief - B. H. Streeter once cal­culated that, apart from the forty days and nights in the wilderness (of which we are told virtually nothing) everything reported to have been said and done by Jesus in all four gospels would have occupied only some three weeks, which leaves the overwhelmingly greater part of his life and deeds unrecorded."

This is from Dennis Nineham, "Epilogue", in John Hick (ed.), The Myth of God Incarnate (London: SCM, 1977), 186-204 (188-9). I can't find the idea that he attributes to Streeter in any of his written works, and Nineham himself does not reference it, so is Nineham reporting an oral tradition? As far as I can tell, Nineham himself did not learn directly from Streeter. Although Nineham did go to Oxford, he was too young to have met Streeter -- only 16 years old when Streeter died in a plane crash in 1937.

On twitter, Brandon Massey speculated that Nineham might have picked it up from his teacher, R. H. Lightfoot, who perhaps reported this as a Streeter comment, which I think sounds quite plausible. 

It is also possible that the "three weeks" comment is a mis-remembered or mis-applied distortion of something that Streeter actually said. What is making me wonder here is that Streeter does in fact talk about "three weeks" in a related context:

Now of the last journey to Jerusalem, and the events of Passion Week, Mark presents a clear, detailed, and coherent account; and this, dealing with the events of, at the outside, three weeks, occupies about one-third of the whole Gospel. The rest of the Gospel is clearly a collection of detached stories as indeed tradition affirms it to be; and the total number of incidents recorded is so small that the gaps in the story must be the more considerable part of it. (B. H. Streeter, The Four Gospels (London: Macmillan, 1924), 424).

And if Streeter thought that Mark's Passion Narrative occupied "three weeks", could he also have maintained that "everything reported to have been said and done by Jesus in all four gospels would have occupied only some three weeks"? So we are now at at least six weeks, and there is clearly a contradiction here, unless the oral tradition also forgets the "three weeks" of the Passion Narrative.

Chasing down oral traditions is notoriously difficult since they only survive, before and outside of oral / aural recordings, in the writings in which they are represented, but this case provides an interesting analogy to first century Jesus research. Nineham's comment in 1977 is at least forty years removed from when the historical Streeter may or may not have made these remarks, rather as Mark is at least forty years removed from what he reports about Jesus, whose actual lifetime contained a great deal more activity than is reported in (pseudo?)-Streeter's "three weeks".