It's certainly worth a try if you have the time to set it up!
However, just warning you: it's possible that auto-block would help out, but it is worthwhile to note that auto-block is going to be overwritten by any attack commands that you put in yourself. So if you are just constantly bashing the attack button you might find the auto block won't work as effectively (not saying it won't work at all, it just might not 100% save you).
Maybe put on auto block on a separate save file and test it out on some Heartless to see if it works for you before you sink a few hours into getting yourself all the way up to Yozora before you realize it doesn't actually help your particular situation.
In terms of attacking time...I'm not sure if this will help, but I find that Yozora actually recovers quite quickly from when you create an opening so long combos are riskier. If he visually staggers you should definitely have enough time to get a full combo in, but not much more unless you get another separate stun in. I found he recovered almost exactly mid-way through my second combo without another stagger--a bit more and a bit less depending on if I used a Shotlock gap closer initially to reach him. Maybe until you feel that you can gauge the timings a bit better it might help just to attack until you see Sora use his finisher move and then back off. You won't get as many potential hits in that way, but then you are far less likely to be stuck in the middle of a combo and unable to guard when you need to. If you are in a form change that is a lot trickier because it throws the timings off. If you stun him WITH your form change, you are probably good to keep using it but if you attack him a bit, then form change, it's far more likely for him to recover mid-combo, putting yourself at risk. I would recommend if that keeps happening to "stock" your form change and switch Keyblades until you are ready to do a combo and then switch back over to it, or just use the form change itself to stun him, do your combo, then stock it by swapping Keyblades once you get one finisher off and back away until you get another opening.
I actually realize you never said what Keyblade you are using, but I would highly recommend either using Ultima, Oblivion or Oathkeeper if you have them. I used Oathkeeper the most (due to visual preference) and found light form to be a HUGE asset.
Also, maybe you know this as well but if you ever get the prompt for Rage form it can actually be quite a good life saver if timed properly. If I get the prompt sometimes I save it for if I need to heal but I don't want to use my mp/items. Or, in some cases it can work as a panic heal if you don't have any other resources at all since entering the form gives you full hp. It also has decently good dodge mechanics and you can use the absorb heart 3 times move spam to cheat and take advantage of some invincibility frames. I wouldn't necessarily recommend hanging out in Rage form if you aren't used to using it, but if you are at 1 hp and don't want to risk timing using an item you can always rage, immediately spam the 3 heart move, limit to return to normal and you SHOULD have >1 hp left or hopefully another opening to heal.