At risk of sounding like a scrub; I'm going to give you an honest answer.
I stopped trying to just guard online. It's a real shame, but I've been focusing on other aspects of my play thus far in to the game. I've been primarily fighting online (my own fault), and I can't Just Guard reliably at all online; so I've just stopped trying for it in my matches. I've focused a lot more on evading attacks (stepping/crouching/jumping) instead of JG'ing, and when something's coming at me and I really want to block/counter it, I just Guard Impact.
The timing for Just Guarding seems really crazy to me, and on top of that I hate how they have it set up to do it. If it was just any input during a small window of frames I'd be ok with it, but you have to actually tap and release the guard input within a certain window; and perhaps it's just me, but that really fucks with my mind - execution wise.
I think Just Guard'ing is one of the most advanced and beneficial techniques in the game, don't get me wrong. It's awesome they put something like that in, but this early in the game; I'm not going for it. Perhaps months in when my brain is trained to the entire's roster moveset; I'll be able to do it more consistently.
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As far as the poll goes, I don't really like the options. I'll vote "Sometimes against slower hitting characters", because if I actually went for them, I would get them some of the time. I've practiced in training mode and even went on sprees of hitting them consistently, but the fact is that during a real match when the pressure is on I don't bother trying because it's not worth it. So right now I practically "never" land them, but if I was fighting with the sole purpose of executing them I would have to say "Sometimes".