This is a tough one to answer since SDL hasn't opened yet and no one really knows what will be a good length of time there. I also haven't been to TDL, but I'll give it a shot
I'll start with HKDL, since I've spent plenty of time there. If you're used to WDW, you will be underwhelmed by HKDL. It is a small park, and it is only one. There is no attached shopping and dining district, but there should be three hotels by mid-2017. Crowds are also not an issue at all, and the combination of short lines and not many attractions means you should be able to get everything done within a day. Having said that, it is a beautiful park with lots of great details and theming, and is such a lovely place to just be. There are also plenty of unique character opportunities with different outfits if you're into that, and plenty of fun photo opportunities. Mystic Point and Grizzly Gulch are amazingly well done and their respective rides are two of the best I've experienced. There are also different dining opportunities like high tea or dim sum. If you'd like to do some table service dining, maybe plan to check out a couple of the hotels (which host their own character appearances throughout the day), and enjoy just taking it all in, I'd recommend 2 days. If you just want to experience the unique attractions within the park, 1 day will be plenty.
I already mentioned I haven't been to TDL yet, but I've heard a lot about it and know people who have been. From what I can gather, the 'castle park' isn't all that different to the Magic Kingdom. TDS is where you want to spend your time. The Tokyo parks get very busy right from opening, with waits for rides and characters getting into 60+ (or even 120+) minute territory. Some shows (and restaurants maybe) are on a lottery system, so you'll want time to try again if you don't get in the first (or second, third etc) time. I would allow at least 2 days for TDS, and maybe 1 or 2 for TDL, depending on how 'Magic Kingdom' like you find it.
At this point, SDL is anyone's guess. China is pretty well-known for its crowds, and I don't think SDL will be any different. At this stage, I would expect big crowds and long waits. The park itself is the most different of all the 'castle parks', and will have a lot of unique attractions. At this stage, I would allow 2 days, but definitely keep an eye on things once its opened for a more accurate idea.