It seems it started in 1928 when the WT taught that some of the annointed remnant would survive Armageddon and would still be on earth to welcome back resurrected faithful ones of old - and therefore, by building and preparing a house that these faithful ones could live in, was a display of the faith that the WT had that these events would actually happen.
Watchtower 15 December 1928, paragraphs 35 and 36
35 Following the great battle, as indicated by the words of the prophet, there comes a time of blessing upon the people, and in this the remnant will have some part. "And the remnant of Jacob shall be in the midst of many people, as dew from the Lord, as the showers upon the grass, that tarrieth not for man, nor waiteth for the sons of men." (Micah 5:7) The remnant are shown in the midst of the people as "dew from the Lord" and as "showers upon the grass", and these words indicate comfort and blessings to the people. This may be taken as an indication that some of the remnant will be on earth even after Armageddon is fought and will then have some more work to do in the name of the Lord and to his praise and glory. The people, having passed through the great and terrible trouble, will no longer look to men for help nor watch for the sons of men to bring them aid and comfort but will turn to the Lord and gladly hear his Word. Some creatures will have the privilege, as the Lord’s agents and messengers, of bearing the message of peace to the people.
36 The remnant of the Lord, according to this prophecy, will go on to triumph in the strength of Jehovah. A lion is a monarch among the beasts of the forest, and none can stand before him. The flocks of sheep are without power against a strong and young lion amongst them. Thus the faithful remnant of God is described by the prophet. These shall be amidst the nations of many people strong and vigorous in the name of the Lord to help those that want help and to point out God’s method of destroying those that resist. The 'hand lifted up against the adversaries' means that God's power will be exercised against all adversaries and all enemies of the people shall be cut off. "And the remnant of Jacob shall be among the Gentiles in the midst of many people as a lion among the beasts of the forest, as a young lion among the flocks of sheep; who, if he go through, both treadeth down, and teareth in pieces, and none can deliver. Thine hand shall be lifted up upon thine adversaries, and all thine enemies shall be cut off." (Micah 5:8, 9) These words of the prophet seem to warrant the conclusion above suggested.
Link to scans
Golden Age 19 March 1930, pages 403 to 407
(main portion begins on page 405, preamble included for reference)
Watchtower 15 March 1937, page 86
(see paragraphs 17 and 18)
s 311-312;
Watchtower 1 June 1940, page 162
(small piece, bottom right, False Reports)
Consolation 27 May 1942, pages 3 to 9
The New World 1942, pages 104 and 105
Let Your Name Be Sanctified 1961, pages 335 and 336
Yearbook 1975, pages 193 and 194
Jehovah's Witnesses - Proclaimers of God's Kingdom 1993, page 76
Watchtower 1 November 1950, pages 414 to 417
(referenced in Proclaimers Book re change in doctrine)
