Time Out/Discipline Question

In our house we mostly use time outs when discipline is required. Usually, the scenario goes like this: Clara is asked or told to do something (i.e. pick up her toys); if she does not want to, she will scream (not continually, one or two loud screams in my direction) and sometimes throw whatever toy happens to be in her hand onto the floor. She knows that we only scream outside. When she screams, I pick her up (without comment or agitation) and carry her to her time out chair.

Here is where my question comes in. Up til now I have been setting the timer and she is expected to sit in her chair until the timer goes off. Then, before she gets out of the chair I ask her why she was in time out ("I was screaming. Need to obey Mommy."), she needs to apologize ("Sorry for screaming Mommy. Will you please forgive me?") and we have hugs and kisses before returning to the situation. She is always ready for lots of hugs and usually says, all on her own, "We need to pick up toys" or "I need to obey Mommy," whatever she didn't want to do beforehand.

Lately, though, she has started getting off the chair before the timer beeps. She will get down quietly, then come running and giggling towards me. She knows she's supposed to stay in the chair and I think that she's trying to see if she can get out of it. But part of me wonders if she is ready for reconciliation sooner. What I have been doing is simply picking her up and returning her to the chair with no comment or interaction, then resetting the timer for a few seconds longer than she had left when she got down. The past couple of days I have had to do this up to 6 times during a two-minute time out on a couple of occasions.

I believe that consistency is very important, but I have been thinking about changing the time out structure. Instead of setting the timer, I would tell her, "You may come out of time out when you are ready to obey and be polite to Mommy," or something like that. Then, when she gets down we would have the same discussion we usually do when the timer goes off. This puts more of the responsibility on her. It gives her an opportunity for faster reconciliation. But I feel like it's also not quite as clear cut as a specific amount of time. If she comes out still grumpy and unwilling to cooperate, of course she would go right back in time out.

Thoughts? Other ideas or suggestions?