When did the silencing of 'h' start?

Question

I am reading (a bilingual version of) Augustine's Confessions, and I stumbled upon:

si contra disciplinam grammaticam sine adspiratione primae syllabae hominem dixerit (1.18.29)

Roughly translated to: "if, against the rules of grammar, one pronounces "hominem" without exhaling the first syllable..." As a native Romance speaker, for whom the 'h' was always muted, this reference caught me off guard!¹

Is Augustine referring to a common spoken error in the non-educated people?

After a quick search on the web:

• Some sources mention "by the time Latin became the language of the Iberian Peninsula (Hispania) [the 'h'] had ceased to be pronounced." Wikipedia dates the Roman conquest of the Peninsula from 206 BC to 19 BC. I don't know when was Latin adopted as spoken language.

• Augustine is from the 3rd and 4th centuries. From the Confessions it looks like the spelling without exhalation is a common error at the time.

• Appendix Probi, possibly contemporaneous of Augustine, mentions "adhuc non aduc" and "hostiae non ostiae" as common mistakes.

Question: Do we know when did the silencing of 'h' start?

_{¹ I never had a Latin course and I have never spoke Latin. I have only heard "Mass Latin". I had always assumed a silent 'h' as in Romance languages, though I now understand the (historical) reason for the letter 'h' in our words derived from "homo" and "historia".}

Answer 1

Before the late Republic

Already in Republican inscriptions we find people leaving off H's, as in Oratia for Horatia, or adding them where they don't belong, as in havet for avet. During this time, knowing where H's belonged and where they didn't was a mark of refinement, and Catullus makes fun of a man who tries to appear educated by saying chommoda and hinsidia.

But from the very earliest surviving texts, there are H's missing that ought to be there etymologically, especially in "rustic" words like anser. It seems likely that certain dialects lost the /h/ sound very early, and for some words this H-less pronunciation became standard across Latin. Even Catullus and his elite, refined circle probably didn't realize that anser "should" properly be *hanser.

In positions other than the start of a word, it was lost even earlier (even in the most prestigious dialects), and we never see nēmo written as *nehemo or liāre as *lihāre.