This might prove helpful:
http://www.jehovahs-witness.com/10/143844/1.ashx
The earliest quote I found was in 1930:
W 01. Nov. 1930, p.332
Speaking of world happenings since A. D. 1914, Jesus said (and his words apply to
Christians living since that date) : “When ye see these things come to pass [as prophesied], know ye that the
kingdom of God is nigh at hand.” (Luke 21: 31) So, inside the lifetime of the present living generation the
Lord Jesus will put into effect for all mankind the value of his ransom sacrifice which he laid down for all. (Brackets in original)