And it is definitely not arbitrary. You are simply wrong.
I’m not going argue the dictionary with you. Here’s another definition from Merriam-Webster:
“based on or determined by individual preference or convenience rather than by necessity or the intrinsic nature of something”
Rather than wasting time quibbling over word definitions, do you agree that Bowles states that he picked his “zero-base” timestamp for “practical purposes” and that no absolute record of time exists?
Bowles:
“1. No exact record of "time" exists;
2. The several clocks were not synchronized;
3. The radio operators were not exact with regard to "time statements" on either radio;
4. The recordings were continuous only on Channel 1, and only while the mike was stuck open;“