There's no such thing. The board code automatically separates posts, even fractions of second (if possible) within each other. Two posts cannot appear at the exact same place, and exact same time. One of them will be posted after the other, according to how the program parses the code, even if they have the exact same time stamp.
But even if that was the case, the answer is to insist on absolute precision, all the time. Problems solved.
The only real problem is editing, which can be done in stealth, and then we require honor.
The rule has always been timestamp, not location of post.
They are the same thing: the time stamp determines the location of the post.
If both people hit "submit" at the exact same second, the board program code will still separate them out, even within fractions of the same second.
Thus, if Person X hits submit at 9:47:33, and Person Y hits submit at 9:47:33, the board will figure out which one was "first", and post accordingly.
In other words, it either picks based on its internal code, or it can figure out who posted at 9:47:33:17 and who posted at 9:47:33:62.
In either case, the post that appears first is the one that IS first, even if the displayed timestamp is identical.
I get what you're saying. We don't see the significant digits. But in the event of equal time stamps, both equal within the sig digits of the software, that same software is forced to place one above another since two posts cannot occupy the same space in this dimension.