I’d rather see this in a separate tag as it just states “We checked the hours on PH, and what the opening_hours tag says is correct / not known if complete”. It just gives additional information to other mappers, not for the hours themselves.
Suggestion:
opening_hours:PH = unsigned | same
A value for closed is not needed, as this has to be part of the opening_hours.
We might want another key, as this one could be confused with the country code of the Philippines.