All the time! From the first to the last second.
I surprised people like this several times when I competed. In fact, one of the best times to (T)KO somebody is right at the beginning of the fight, in the first few seconds. Many fighters, even professionals, aren’t at 100% mental focus then. Blows they shrug off in the second or third round can put them down if you get one in right away, simply because they need time to “warm up” inside their head.
So if there’s a lesson here, it is to work on your intent before the first blows are thrown. And keep your guard up!
Another lesson might also be to learn some cool dance moves to celebrate your victory. The funky chicken has been out of style for decades… :-)