This one never gets old.
- Exceptions to the rule: Hosea 6:1-2; Zechariah 14:7. IIRC there are other examples as well.
- The way that “yom” is combined with a number (yom ehad, or “day one” — no definite article) in Genesis 1 is unique to Genesis 1. Elsewhere it’s always hayyom harison or hayyom hasseni — with the definite article.
- The context (large, grand scale events) of Genesis 1 is completely different from the context elsewhere (day to day dealings of human beings). See this excellent takedown by @Socratic.Fanatic back at the start of September.
- There are some very good reasons to believe that this “rule” is a YEC fabrication. It is only ever cited by YECs, and even then only ever in the context of trying to attack the day-age, gap or framework interpretations of Genesis 1. It first appeared in YEC literature in the 1970s and was unheard-of before then.
- Outside of YEC circles, no Hebrew scholar acknowledges its validity.
See: also this paper by Rodney Whitefield.