I had one child that a time-out had to be away from people (my extrovert), and one for whom it needed to be a tight embrace (my introvert). Not a hug, really, but a tight hold to let him get control of his overwhelming emotions. We started them as soon as emotions ran high, so earlier than 29 months, I'm sure.
In both cases, we treated it as a "time out from the opportunity to do what you're doing until you can control yourself." When self-control returned, the time out ended. Period. None of that "1 minute per year of age" stuff. To me, that's about punishment, and that's not positive discipline. I focused on the time out strictly as a tool for getting past the overwhelming emotions, which is why they were acting out. I wanted to reward self-control, since to me, that's the ultimate goal of a time out.
We rarely use time outs now, since even the 4.5yo is much more able to manage his emotions. If they are overwhelmed now, it's usually because they are hungry or tired. Then I give them a time out while I get a snack together.
