I got this tonight after four hours of non-stop grinding, and I've come up with a method that anyone struggling with this should try. It builds upon MattiasAnderson's solution, so most of the credit goes to him.
Basically, what you want to do to nail the block+dodge combo he talks about is this: move your lightsaber hand in a circle constantly while trying your best to chain perfect/good dodges together. That's it. Make the circle decently wide but not too wide and don't spin super fast. This sounds too cheap to work, but trust me, it will get you both block+dodge and parry+dodge (!) combos quite frequently, while requiring little effort from you other than dodging. You should also not try to see which direction to dodge in most of the time, unless you have super fast reflexes. Just remember the preset dodge order I'll give you, and stick to that. Yes, this leaves a lot down to luck, but when it works, it really works.
So here's how this played out for me.
1. Start spinning the saber hand, then dodge right-right-left-right. Sometimes you'll get a clash skip before the third dodge, which is great. If his first move is a swing from the right, that's not a huge deal even if you dodge into it. However, if you get a dodge off, and then get hit, you should restart. This is because getting three dodges (or any defensive move) in a row gets you a big combo multiplier, which is really important.
If you get a clash around 7 seconds, that's fine, but any later than that and you should restart. Whether you skip the clash or not, Vader should have 3-5 items behind him. Three is bad, but it works. Start hitting him right away, alternating between horizontal and vertical swipes (very important!). Pick up an item (preferably two) and throw before he staggers the first time. While he recovers, pick up 2-3 more to finish him off while hitting him some more. If he staggers a third time, that can be a big time loss.
You should finish this part at anywhere between 12.5-18 seconds. 18 is really pushing it while 12-13 will give you a little bit of room for error later on.
2. This is where things often go very wrong. Everything from phase 1 still applies, but your dodge order should be right-left-right-left (and so on, as long as needed). It's very important he has a lot of stuff behind him on this one. I normally play it safe here after the clash (or no clash) by letting him stagger three times, hitting him with lightsaber strikes and some objects in between each one. That's why you need a lot of stuff to throw.
If you did super good here, you'll be around 29-31 seconds. anything up to 35 or so is fine though, anything above that and you'll need a very good phase 3.
3. This is where the nerves will start to show. Don't choke (like I did, several times...)! Dodge order is right-right-right-left. The only thing that matters is that the tower thing is visible behind Vader though. It can be very hard to finish him off in one go here, so you really have to make sure you focus on alternating your swing direction. Try to only throw one of the objects before the first stagger, then the rest after he recovers. He will always stagger a third time, after which you'll have to quickly whittle down his remaining health before the time runs out. After that, just finish him off.
I should add that even though the results screen rounds your time down, getting say, a 59.28 (like I did once) will NOT give you the achievement. You have to be below 59.
Good luck, and feel free to comment if you have any questions