I noticed a number of fallacies with the 1914 doctrine. The 607 BC one is the one that's most blatant. But, where does it say that we multiply the 3 1/2 Times by 2? I couldn't find that. And, "a day for a year" is a very specific phrase that refers only to a specific punishment meted out when Moses would wander 40 years for the 40 days of rebellion. That has no other application. For sure, it is presumptuous to apply that to the present.
Then they messed up on the length of the "days". You see, most years do not only have 360 days. That is the number they use, which is automatically going to lead one to the wrong date. Most years have 365 days, and the average (including leap years) is 365 1/4 days per year. That lengthens each "time" by five years and the quarter.
Assuming the 3 1/2 times are multiplied by 2 (which itself is fallacious), you arrive at 2,556 3/4 years, not 2,520 (and that again misapplies the "day for a year"). Starting with 587 BC, you would arrive at early 1971 as the starting point, not 1914! Did anything notable start in early 1971? I don't think so.
Perhaps whoever wrote that needs to go to first grade and learn math and science. First question: How many days does a regular year have? A leap year? How often do leap years come up? Perhaps then they would come up with a better answer--and allow for that maybe they weren't supposed to multiply the "times" by 2 after all.