When will a state open up to allow a level 31 HQ join?

Newly created states do not allow for higher levels HQ. The highest player in the state is what will auto set the limit for allowable players to come to the state. I believe the default is around 25 and then as players evolve it will move up. Once the state has had their first svs the governor can also bump it - but they aren’t likely to bump it to high level players to risk losing control of the state.