Dream Drop Distance Confused about Shadowslide

I know it's supposed to be really simple to use, but I have no clue on how to use this thing properly. I just beat the game (yes, only on Normal mode....makes me afraid to think how bad it'll be on Hard. Might want to get some Julius practice in now), and the whole time Riku had his Shadowslide skill I could not get it to work when I wanted to. I did manage to use it a few times, but I don't know how, the most that happened was I hit Y, he used the skill, and I attacked. The skill says to push Y just before you get hit, but is there an easy window to tell with that? Or does it differ with each attack? Every time except for the accidental moments it DID happen I just ended up guarding and using my counter move. I was just wondering if you guys had any advice on how to use this skill so I'd be better prepared for the future, because it seems like it could come in handy in a big way.

 

Unless you get a HARD read or your opponent telegraphs their moves absurdly early, it's pretty hard to nail it consistently. That said, it's virtually useless compared to Dark Barrier. The only time I got it, and perhaps the only time it was worth the trouble, was during the fight with Julius. His hitbox during the punch rush is big enough and out long enough that I would mash out the Shadow Slide about 1/2 the time.

 

I did manage to use it a few times, but I don't know how, the most that happened was I hit Y, he used the skill, and I attacked. The skill says to push Y just before you get hit, but is there an easy window to tell with that? Or does it differ with each attack? Every time except for the accidental moments it DID happen I just ended up guarding and using my counter move.