Ah yes, working backward to prove your doctrines- what a great concept.
This is like deciding how big your tax refund should be, based on your needs,
and working backwards to determine what your income last year will be.
My studies have shown me that any group could use the Bible and history to
come up with any date for their important events. You could even shorten the
year to 360 days if your math is not quite right, or fudge one year if your first
calculations forgot that there was no year "Zero" in the figuring. You could
prove that man is 6000 years old and establish things the Bible doesn't even
mention, like "how long a creative day" is, or you could apply "a day for a year"
to anything you like. With a two thirds vote, you could change a generation
to a different era, or decide that it is a vague concept.