Here are 10 references spanning about 30 years:
1961 Feb 22 p. 7
That now-operating kingdom in heaven will, within the twentieth century, cleanse the entire
earth of wickedness... Can you not see that the twentieth century is the century indicated by the prophetic language of Matthew
24, Mark 13, Luke 21, and 2 Timothy 3?
1961 Feb 22 p. 8
...is it not only logical that whatever else is recorded in these above-mentioned Bible chapters
must also come upon the twentieth
century? ... Revelation 16:16 calls it the "war of the great day of God the Almighty," Armageddon. This war will come in the twentieth century. ...Now is the time to heed Bible prophecy
concerning the twentieth century and live forever in the sunshine of
God's new world.
1962 July 22 p. 32
But how many realize that it contains information of special interest to those of us who
live in this climactic twentieth century?
Nations Shall Know That I Am Jehovah (1971) p. 216 para.9
"Shortly, within our twentieth
century, the "battle in the day of Jehovah" will begin against
the modern antitype of Jerusalem, Christendom."
True Peace and Security (1973) p. 72-73 para. 7-8
"What does [God's] word say regarding our day?
It describes events of this twentieth
Your Kingdom Come (1981) p.11
...now in our 20th century, we have
come to the time for harvest — "a conclusion of a system of
things, and the reapers are angels"!
Watchtower 1984 March 1 pp.18-19
"Some of that "generation" could survive until the end of the century. But there are
many indications that "the end" is much closer than that!"
True Peace and Security (1986) p. 69 para. 3
"The Bible clearly describes events of this 20th century"
Revelation Climax (1988 - removed from the
1996 revision) chap. 34 p. 246 par. 1
The John class today also wonders with great
wonderment as events unfold in fulfillment of the prophetic vision. If people
of the world could see it, they would exclaim, 'Incredible!' and the world's
rulers would echo, 'Unthinkable!' But the vision becomes a startling 20th-century reality.
Watchtower 1989 January 1 p.12 (loose copy magazine):
"He was laying a
foundation for a work that would be completed
in our 20th century."