One question on the knife: Since you are specifying that the knife is designed for defense, does it have a basket hilt or an oversize guard? If so that changes things. A basket hilt is almost a small shield, and you can punch block another hand weapon with one rather easily without using the blade at all.
Just an oversized guard. My whole thought process was tied up with that intriguing little cut into the metal near the hilt that is designed to snag, trap, and twist the larger weapon out of the other's hand. I've never found a place to use that and it seems like such a useful little inclusion in smaller weapons. Sort of the small shall endure type thing that I love--but in this case...
Another thing that comes up... Can you parry with a basket hilt? I guess I think of the basket as protection of the fingers beneath--not as a parry device.
If its cutting through Time, you can do all sorts of fun things to block a blow that neatly sidesteps physics entirely. It could slash a short term rift in space-time that (due to the necessity of normal cause/effect in the universe) cannot be passed through edgewise. The effect would be a floating line of Do-Not-Pass. The possibilities are endless when space/time manipulation is involved.
The main character receives it as a gift at the point her powers manifest. So she has only the simple comment that it does that. The knife is minimized and causes her problems when she assumes it will help her with her current delimima. Since she has no training or understanding, it only gets her into hot water and doesn't solve her problem at all. The space/time travel thing is used by an older character with years of training. For my main charater she will not obtain full use of the knife for at least two more books. We must grow into our magic--gifted magic knifves or not--at least in the world I created.
Frankly, the discussion did a great job of bringing me back to reality and the true capabilities of my main character. She's not designed to be warrior woman, even if she were completely up to speed with her magic abilities. Not that she needs rescuing--it's just not going to happen with her weapon or magic skill at this point of her life. She has to use her wits and her problem solving abilities to get the job done. Who knows with training and if the need arose for later books---if I consider a series.
or maybe hyper-age the sword so that it turns to rust on contact when the MC blocks/parries?
Oh, oh, oh--that would be cool. I'll keep for later use! thank you!