Its not about how you do it, so well as you can do it and react with it. I'm sure i'll be corrected if i'm wrong, but playing marth is the sh to first fa not the fastest hand movement you'll need? obviously things using both hands have closer timing, but as far as moving your hand/finger to do something, all the speed you'll need is this shdf. So work on just being a little faster, finger speed is muscle memory and use, so practice if you need, but thats the bar to reach. If your using Z, try pressing Z earlier in the jump for the attack. if thats not it, your just messing up the timing, and you should be carefully watching the sword and when the animation finishes. Too early and you won't get the second attack at all, too late you won't get it all the way around. its boring, but just set it to no time a level 1 comp and get determined to figure it out =P
-True