From my understanding, curfew for teenagers 17yrs or older in Ohio is 1am-5am but apparently our city has their own ordinance and curfew starts at 11pm. I explained this to the officer that I had given him permission because I was not aware that our city has its own law. A ticket was issued anyhow.
I live in Ohio also, there is no statewide Curfew Statute. The 1-5 time frame you reference pertains to drivers and probationary driver licenses, etc.

Municipality's can enact their own curfew ordinances pursuant to the Police Power granted by the Ohio Constitution Article 18: Section 3: commonly known as "Home Rule".

Obviously, the officer did not believe his "lawful activity" defense. It seems he could have waited and contacted you then or later, as it is a Minor Misdemeanor and has 6 months to initiate a prosecution. He of course will need you as a witness to verify he had permission. Once that is established, there should be no reason for the Court to find him guilty.