Only thing is, the value is rounded to the nearest second! I would have expected it to return decimal places based on the available accuracy of the file system.

The number of seconds since the 0th second on January 1st, 1970 is a common unix time stamp. That's why it doesn't "return decimal places based on the available accuracy of the file system". Because it's a *nix time stamp, not a universal time stamp (although it is often used as such)