W.T.
I tried that with my 2.5 year old and it didn't work. At all. I had to engage way too much with him to make it worth while. I was stonefaced and just repeated the "rule" and it was still a battle with him doing silly dances and saying hysterical things that almost killed me!
So, we gave them up and I found another consequence that worked much better for me. I removed myself from him for 2 minutes. For example, he'd hit his baby brother. (I prepared him for this consequence in advance too). I'd say, the rule is "no hitting" and tell him that it looked like he needed a little alone time right now. I'd go in the kitchen. Set the timer for 2 minutes and ignore him. No eye contact, nothing. I'd just putz around, talking to the baby and maybe doing a few things that my 2 1/2 year old would have helped me with (like take the mixing bowls out) just to make it clear that mama was doing things all by herself.
It worked. I felt kind of mean because it really bothered him. But, he stopped the behaviors within 1 or 2 times and we haven't used any of it since.
Usually his hitting was because he was tired, so I'd redirect and try to get him to nap or rest or whatever we needed and if that didn't work, I'd give him his "alone time" (he'd follow me around, but got zero acknowledgement) and as soon as the timer went off, we'd be right back to normal. Like nothing happened.
Good luck.....don't know if it will work for you, but battling time outs was not working for us, no matter what I tried.
I don't think they work for everyone, nor do I really agree with them now.
here is a great link by Dr. Sears about his feelings on time outs and alternate suggestions: http://www.askdrsears.com/html/6/t061900.asp