The timing window is small... but after I found out when to use 2B, I almost never miss it now. So try to get the timing yourself, it's surprisingly easy to get it to hit once you do in my experience.
I time mine so that as soon as the opponent is flat on the floor, I press 2B. Just watch the opponent and try adjusting the timing for doing 2B. (And if you're mashing 2B, don't.)