Today this book publishing shibboleth is a myth

Hi

Please help me with the queries about the definition below. Thank you.

1: How am I supposed to read the sentence "today this book publishing shibboleth is a myth"? Is "book publishing shibboleth" meant to be a single phrase?

2: I think in this sentence fragment, "some truth in the shibboleth that crime does not pay" "shibboleth" is used in the sense "PLATITUDE", and not in the sense of "TRUISM". Am I correct?

3: What does the phrase "hour dividing mankind" mean?

shibboleth
1 a : a word or saying used by adherents of a party, sect, or belief and usually regarded by others as empty of real meaning the old shibboleths come rolling off their lips — Joseph Epstein b : a widely held belief *today this book publishing shibboleth is a myth— L. A. Wood* c : TRUISM, PLATITUDE *some truth in the shibboleth that crime does not pay— Lee Rogow*
2 a : a use of language regarded as distinctive of a particular group accent was...a shibboleth of social class — Vivian Ducat b : a custom or usage regarded as distinguishing one group from others *for most of the well-to-do in the town, dinner was a shibboleth, its hour dividing mankind— Osbert Sitwell*

M-W's Col. Dic.