Perhaps this would be of some use (from the article "KNOWLEDGE AND FAITH REGARDING CHRONOLOGY"):
But let us suppose a case far from our expectations: Suppose that A.D. 1915 should pass with the world's affairs all serene and with evidence that the "very elect" had not all been "changed" and without the restoration of natural Israel to favor under the New Covenant.(Rom. 11:12,15.) What then? Would not that prove our chronology wrong? Yes, surely! And would not that prove a keen disappointment? Indeed it would! It would work irreparable wreck tothe Parallel dispensations and Israel's Double, and to the Jubilee calculations, and to the prophecy of the 2300 days of Daniel, and to the epoch called "Gentile Times," and to the 1260, 1290 and 1335 days, the latter of which marking the beginning of the Harvest so well fulfilled its prediction, "Oh, the blessedness of him that waiteth and cometh unto the 1335 days!" None of these would be available longer. What a blow that would be! One of the strings of our "harp" would be quite broken! Watch Tower Reprints, p.5368 (December, 1913)
Hope this helps...