Comma usage after the start of a sentence beginning with time

Question

It has been an ongoing debate in my office among managers that there should be a comma used after a statement of time.

Ex.

At 1135 Hrs., (Subject) Was observed doing something that he shouldn't have.

It is this comma after the abbreviated hours we are having a debate over. Is it proper to put it there or is it not needed in this instance?

Possible duplicate of Comma after introductory phrases (see kiamlaluno's answer, and the Kolln article). Though the use of Hrs is unusual in civilian life, and the period after Hrs can lead to messy double-punctuation ('BrE' tends to leave off periods where ambiguity doesn't ensue). // Conclusion: << At 11:35, X was observed doing something that they shouldn't have been doing. >> — Edwin Ashworth, Sep 12 '19 at 16:22

score -1 · Answer 1 · answered Dec 15 '18 at 23:12

I would say a comma is required, since one could view "At 11:35" as a dependent clause. This would be apparent by rephrasing the sentence:

(Subject) was observed doing something that he shouldn't have (at 11:35).

A dependent clause preceding an independent clause must be separated by a comma (see rule 4a, grammarbook.com).

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