Learn English – What does the phrase “half seven” mean

If your question is about the use of of before a day of the week, then the answer is that, at least in some varieties of British English, it is used to mean ‘at some time during, in the course of, on’. This use has its origins in Old English and has been in continuous use for 1500 years. Here are just three examples from the Oxford English Dictionary:

Always of a Monday morning he was on the dock a good half-hour before the expected arrival of the boat for town.

Mr. More . . . expounds the universe and the Platonical soul to 'em in St. Clement's Church of a Monday afternoon.

Kippers of a Friday, roast of a Sunday.

The Oxford English Dictionary's earliest reference to the phrase is 1787:

e. as neat as a (new) pin.
1787 Columbian Mag. I. 636 [He was] neat as a new pin. 1801 J. Wolcot Wks. (1812) V. 35 How neat was Ellen in her dress! As neat as a new pin! 1849 Thackeray Pendennis I. xiii. 118 Major Pendennis, whom Miss Costigan declared to be a proper gentleman entirely,..and as neat as a pin. 1933 L. A. G. Strong Sea Wall 245 Sheehan's pride was to have his cottage as neat as a new pin. 1961 Dog World Apr. 30 In the morning we leave the room looking as neat as a pin!

Although the first cited reference is a Philadelphia journal, the second cited reference is from the British author John Wolcot in 1801. I think we can assume from this, and many other British sources from the 1840's onwards, that the term has long usage in both American English and British English. Consequently it would be appropriate to 'put it in the mouth' of a speaker of British English in the 1930's.