Outside of the published hours, the airfield would be unlicensed.
Rubbish, its is either licensed or its not! It may not fulfill the conditions of its licence, but it does not go away.
Aerodromes have either a Public Licence or a Private Licence. If its private then you have no right whatsoever to go there without the owners permission. Technically PPR should be the norm at any Private Aerodrome.