To be clear, when talking about an acceptable level, I haven't come near mastery of this move. And concerning this particular technique, I don't have very high ambitions, as I'm focusing on other moves at the moment. It's currently good enough for what I use it for (part of a gambling demo), and it's flown by all spectators so far.
It may very well be that our second deals look quite similar, but that you have higher standards than I do. If you're aiming for a Marlo/Nash/England level, then "acceptable" is a few notches higher than if you're aiming for a 30-second segment in your gambling demo.
I'm planning to put up a video of my progress on several sleights, to get some constructive criticism on them, sometime in the near future. You'll be able to see for yourself whether there's really any difference between your second and mine.
It's difficult to say how long it took me to arrive at the level I am now. I first started practicing it (though not very seriously) about 1 1/2 years ago, when first starting out with cards. About a year ago I started practicing it a little more seriously, though it was still on and off practice. To be honest, at the moment I'm only practicing the strike second to stay consistent (it's crazy how quickly your skill level can deteriorate with this sleight), not to get better.
Probably the best advice you can get is the one Jason England mentions in his Penguin Live Lecture (as I don't own it, I don't know whether he talks about it in his T11 1-on-1). Does "dealing strike tops" ring a bell?