The WT isnt alone...I didn't realize how many nut jobs use this math to forward their prophetic agendas. Dates start all over the place and end up in around our time, give or take a few hundred years..
http://www.google.com/search?hl=en&rlz=1C1GGLS_enUS360US363&q=7+times+2520+years&start=10&sa=N
The WT doesn't even make page one on google with their 2520 theory. Have to go to page two to find them...Of course they lie right off the bat with this quote:
DECADES in advance, Bible students proclaimed that there would be significant developments in 1914. What were these, and what evidence points to 1914 as such an important year?