I generally get the just frame quite consistently after A+B for the longest possible combo, and can usually pull off the punishes pretty consistently (at least when I'm in practice, and properly adjusted to whether it's online/offline). But I've only recently started being able to semi-consistently hit the 66:B just frame after 1K. And goddam, it actually makes Voldo a ringout beast. 1K is completely safe, not horribly slow, TC's, and has really decent ringout distance. When someone's back is to the ring, you can just keep poking them with 1K when you're at + frames and it really makes them panicky about doing anything. Then you can also throw out 1K at disadvantage hoping that they tried a high or grab. And you can try to step something and hit with 1K post whiff. Today I was playing sword lord on XBL, and on ringout stages I would almost always get one 1K ringout per match. If someone's back is directly to the ring, you can also do the 236B/1K mixup. Although you gotta be careful, if they have a reverse ringout move they can do from crouch, you're free if 236B is blocked. Overall moral of the story: to be a good ringout character, you don't need a ton of good ringout moves, just one.
Another random piece of info: you get can get ringouts from even farther than 1K with BS 22B, although the timing is much trickier. It's especially lethal because your step is so great in BS and 22B comes out directly from there. The timing you want is NOT the fastest timing, if you do that it hits them too early, pops them in a weird way and the second hit doesn't connect. However if you delay just the right amount you still get the 66:B double hit but higher on the character than from 1K, so you get awesome ringouts. The ringout range on this is definitely better than BS 4KA although this move is slower and harder to pull off.
Back to the original topic: you don't really need to hit the two 6's all that close together. As far as I know you can't fail to hit 66:B because the 6's are too far apart; what will happen is that Voldo will just take a step forward and then do 6B if the 6's are too far apart. But as long as you are getting 66B and 66:B, the problem is that the second 6 and the B are not simultaneously. Just aim to hit them at the exact same moment, it's not hard because you are hitting them with different hands. Hitting it a few times is no big deal, the trick is getting the highest possible consistency in controlling whether you get 66B or 66:B. The best punishment combo for Voldo is 66:B, 66B, 66:B, (one of several enders), and to get the first three hits you need to do that exact sequence.