I did some research after reading this thread: http://www.jehovahs-witness.net/watchtower/bible/246165/1/Using-Microsoft-Excel-to-disprove-Watchtower-Theology-Authority
and realized there have been some flip-flops in the Watchtower's interpretation of Daniel's prophecy.
Here is the interpretation from 'Pay attention to Daniel's prophecy' (1999) pg.301:
PROPHETIC TIME PERIODS IN DANIEL
Seven times (2,520 years): Daniel 4:16, 25 October 607 B.C.E. to October 1914 C.E. (Messianic Kingdom established. See Chapter 6 of this book.)
Three and a half times (1,260 days): Daniel 7:25; 12:7 December 1914 to June 1918 (Anointed Christians harassed. See Chapter 9 of this book.)
2,300 evenings and mornings: Daniel 8:14 June 1 or 15, 1938, to October 8 or 22, 1944
("Great crowd" emerge, multiply. See Chapter 10 of this book.)
70 weeks (490 years): Daniel 9:24-27 455 B.C.E. to 36 C.E. (Messiah's coming and his earthly ministry. See Chapter 11 of this book.)
1,290 days: Daniel 12:11 January 1919 to September 1922 (Anointed Christians awaken and progress spiritually.)
1,335 days: Daniel 12:12 September 1922 to May 1926 (Anointed Christians attain a happy state.)
And here is an earlier interpretation:
From 'Your Will Be Done On Earth (1958) pg. 371:
PROPHETIC "TIMES" AND "DAYS":
"SEVEN TIMES" or "the appointed times of the nations" (Daniel 4:16, 23, 25, RS; Luke 21:24): Began in 7th lunar month (Ethanim-September-October), 607 B.C.
Ended in 7th lunar month (September-October), A.D. 1914
"TIMES, TWO TIMES, AND HALF A TIME" (Daniel 7:25; 12:7, RS):
Began in first half of November, 1914
Ended May 7, 1918, at arrest of Watch Tower Society's officers and companions
(Compare the 42 months of Revelation 11:2.)
"A THOUSAND TWO HUNDRED AND NINETY DAYS" (Daniel 12:11, La):
Began the end of January, 1919
Ended the first half of September, 1922, at the second Cedar Point (Ohio) convention
"THE THOUSAND THREE HUNDRED AND THIRTY-FIVE DAYS" (Daniel 12:12, AT):
Began the first half of September, 1922, at the second Cedar Point (Ohio) convention
Ended in the month of May, 1926, at the London (England) International Convention
"TWO THOUSAND AND THREE HUNDRED EVENINGS AND MORNINGS" (Daniel 8:14, RS):
Began in the month of May, 1926, at the London (England) International Convention (May 25-31) Ended on October 15, 1932, with the official publication of notice in The Watchtower
These are two contradictory versions, and it is just a hopeless shambles, which leads one to the possibility that Daniel wasn't actually referring to the JW's in the first half of the 20th century at all...