If any of your shadows were outside the bubble, you would have more time, but the inside ones should still be moving at the same speed relative to you, I think.
I had also considered that atium might work, because you could theoretically see the bullets shadow leaving the bubble, and you could just adjust your aim until it went the right way, but I'm not entirely sure if that would work, because atiumshadows don't take into account what the person atium might do. For example, if your a mistborn burning atium, and there's a coin on the ground, you could Push on it in many different directions or at different times, which leads to a lot of possible futures for the coin, but its shadow doesn't actually split.
Sorry, I don't quite understand the question. Could you rephrase that?
My understanding of electrum is that the shadows split no matter what. Atium doesn't split because you see what someone else is going to do, and they are going to do that no matter what, unless they can see the future. The way I think of it is you have an arrow going from the atium user to every other object around them, because they can see the future of those objects, but none of those objects can see their own future. Add another atium burner and it creates arrows both ways between atium burners. As soon as you have an arrow going both ways, it creates a feedback loop that causes a bunch of shadows. For electrum, the arrow is automatically in a loop, because it goes from you to yourself.
This WOB isn't explicit about there being multiple shadows, but it seems to imply it:
So, looking at this, there might not automatically be a lot of shadows. It seems like maybe looking at the shadow causes it to split, because now that you see this future, you no longer have to follow it, so it creates other options.
One way I think of it is that there's your base shadow, which shows what you would do if you weren't burning electrum. Because you see that, you can choose to change it, so that creates more shadows, showing options that you could do instead. You could call them second generation shadows. These shadows show things you might do if you were able to see the first shadow. In continues on like that, where each set of shadows takes into account the fact that you can see the ones before it. It probably stops once there are too many shadows for you to consider all of them.
And, yes, this is my own theory. I haven't seen anyone discuss electrum/atium in bubbles, except for that one WOB you brought up. It's really all theoretical, especially since we haven't see electrum used other than as a counter to atium. I do think it might be possible, if very difficult.
Ooh, I didn't think about using zinc before! I would imagine that you would need a lot of zinc, and you would also need to already understand how time bubble refraction works. But yeah, that could totally be a better way of doing it.