Can you turn off wifi for certain hours ?

There's not a built in timer for that function. All you'd do is turn on airplane mode to do that. Is the issue data? Or notifications? If it's data Airplane mode is probably your best bet, notifications you might want to look into Do Not Disturb.

There is no way to automatically do this for an iPhone.

Their may be an app that can help with that? There's no setting that Apple would have. Those darn teenagers!