If you just mean fiction that uses some informed version of genuine scientific theory in a field, fair enough. To me, though, that's not 'hard SF'. It's impossible to establish 'scientific accuracy' in fiction if the field of science discussed has not established a 'truth' of its own.

Yes, that is what I mean, I guess. Hmm. I'm not very good with definitions.

I mean, you're not going to accurate anyway once you add the equivalent of time travel or what-have-you, but you can be rigorous.