"the convoluted selection of ‘2520 years’ doesn’t even have any direct biblical basis." I would suggest it doesn't have any indirect basis either.
The Book of Daniel is agreed by a consensus of Scholars to be a thinly veiled political/religious tract against Antiochus Epiphanes 1V, no way was the seven times/years envisaged by the writer to be any longer than what the Chapter says, seven years of madness for the King. "Daniels" prophecies were supposed to happen very soon, apart from the vague apocalyptic stuff.
To extrapolate 2520 years from "Daniel" is a twisting and misuse of Scripture, and you have to be deranged to accept it.