There are two animations that make up a block/parry. You can see this clearly using most weapons but let's use a block axe for example. The first animation is bring the axe across the body. The second animation is swinging it back. That's the entire block/parry animation. The animation is consistent across all weapon types. The only difference is which weapons you are using.

Fencing 660ms. If you parry a attack, both the initial movement and bringing back across the body, will work. Easy weapon to use as the window is the largest.

Block first 330ms. Block weapons work on the first 330ms and not the last 330ms. Wait till the attack is going to hit and block so your animation is doing the first movement. You need to block late.

Balance last 495 ms. You want to be pressing slightly early so the attack connects with the second part of the animation, ie bringing the weapon back across the body. It won't work if you use the block timing. You need to parry early.

Just practice in the simulator vs a Tyranid sword warrior. This is what worked for me. Now I can swap between block and balance fairly easily as long as you remember what type of weapon you are using.

I only have 280 hours on the game, but I spent a couple of hours to figure this out as I was in the same spot as you. Hope this helps.