Utilising yet another method of calculation, the Seven Times are explained as 'lunar' days converted to 'solar' years. Taking a 'time' to be equal to a 360 day lunar year, seven times are 2520 days, which become 2520 lunar years. However, from 607 B.C. to 1914 A.D. is 2520 solar years, so this prophecy is worked out as 1 lunar day equalling 1 solar year.
1) There is no such thing as a 360-day lunar calendar. The Jewish lunisolar calender was 354 days in length, with an intercalated month every several years.
2) The Jewish 360 +4 calendar was solar/schematic, not lunar. It consisted of 360 monthly days (twelve 30-day months divided into four seasons), with an extra day lying in between the seasons as a marker of the seasons (i.e. the equinox or solstice). Eventually by the middle of the second century BC, this extra day eventually came to be reckoned as belonging to the months, with one 31-day month every season (as it is in Jubilees and the Qumran calendrical texts; the Book of Luminaries in 1 Enoch has the older system).
3) Even though the older reckoning omitted the solstices and equinoxes from the months, such that 12 months would contain 360 days, it still counted them in the yearly reckoning as they were essential to make the sabbatical aspect of the calendar work (as 364 is divisible by 7, allowing every year to begin on a Wednesday -- the day the sun was created in Genesis). The calendrical texts in the Dead Sea Scrolls contain detailed, complicated schemes intended to synchronize the two calendars (the solar/schematic with the lunisolar).
4) So among other absurdities in the Society's interpretation of Daniel 4, it doesn't realize that the 360 +4 calendar counted the solstices and equinoxes in the yearly reckoning, such that "seven years" would yield 360 monthly days and seven years' worth of solstices and equinoxes. The error is quite apparent in the use of Revelation 11:2-3, for the 1,260 days are explicitly "forty-two months," and thus don't count the days that may lie in between the months. So this means that the JW reckoning of the "seven times" is off by 28 years if it were to use the actual calendar that the 1,260 (3 1/2 years), 1,290 ( 3 1/2 years + one more 30-day month), and 1335 (3 1/2 years + 2 1/2 30-day months) periods pertain to.
5) The solar/schematic calendar still fell a day short per year, so it is unclear whether it had its own system of intercalation or whether it's synchronization with the lunisolar calendar was imperfect.