For the 66 5A timing, first go do gashou and see Haz hind legs (if you're on 1P side, its his left leg) and watch how the leg gonna be 'restore' back to neutral (make sure you hide Input Display or else you can't see the leg). After you get used to it, try 66 5A on neutral and get used to it. If the 66 6A comes out then you need to input it a biiiit slower the 5A.
Then try do 3C>66 Gashou>66 5A. If the dashing overhead comes out, then that means you need to input slower but its a step in the right direction IMO.
I don't master it yet but this is the easiest way for me to do it. I'm sure other people will have other tips to do it consistently. If you can do Hiren loops in Extend, then this part isn't that hard (and I suck at Hiren loops lol)