It is quite simple:
1. The ATZ of a government aerodrome is active at such times as are notified (usually H24).
2. It is a breach of Rule 45 to take-off, land or fly within the ATZ without the permission of the relevant air traffic control unit.
3. If the relevant ATC unit is closed and it is not possible to obtain permission to fly within the ATZ then to do so is a breach of Rule 45.
4. Get used to it.
Locally based operators operate with the permission of the ATC unit although the unit may be closed at the time of operation. Rule 45 does not say that permission must be sought by radio.