The tutorial literally straight up says “there’s no timing window, as long as you are holding down left/right when an enemy attacks.”
Guide to Perfect Dodge
Perfect dodge is done by tapping the dodge button as the enemy attack begins the wind up, it’s a very odd timing window and is not similar to any other games where you would normally tap the dodge button just before it lands.
Normal dodges are weird but if you find yourself getting hit whilst still doing the dodge animation, it’s possible that you let go of the dodge button too early. You need to hold it down before they throw an attack and continue to hold the button down until the animation finishes. Generally I just try to strafe around the target but this doesn’t always work in tight spaces (Yes I know this is practically everywhere).
Combat is methodically slow paced so this shouldn’t throw you off or cause you to get hit if they swing a second time, just get ready to move into a second dodge. With all that being said, the mechanic itself is very strange and dissimilar to any other game with a dodge for melee and you almost have to retrain your brain.