Difference between "opening hours" and "open hours"
Solution 1:
The part that you haven’t stated is that in common business usage, “opening hours” refers to the period the business is officially open. The phrase “open hours” isn’t established in business lingo.
“Open hours” could be interpreted as those times the business happens to be open - which, as one might expect, would often be the same as the official hours. Alternatively, since “open hours” hasn’t acquired a fixed meaning in business, it could be coerced to reference other definitions of “open” (e.g. empty, honest, etc).