Help with almost 3 year old acting out after new baby?

I am going through the same thing right now I have a 2 1/2 yr old daughter and a 5 week old son. We figured out real quickly that we had to stop her behavior quickly. It's not fun, but it has improved for us a lot. Time out is a big thing, and she gets that for any bad behavior she doesn't stop once asked and given one threat of timeout. These things include yelling, screaming, hitting, etc, etc, etc. Also, her time doesn't start for time out (the one minute for every year old they are) until she calms down because once we put her in time out she is MAD and will scream and yell. Once she calms down she gets 2 minutes or so then my husband or I go in and talk to her about why she is in there she has to repeat why she is in there and apologize to whomever. In the beginning it feels like you are being SO mean to the older one and so nice to the other, but you have to discipline so try not to feel bad. Also, I know you have cooking, cleaning, etc to do BUT your son needs some one on one mommy time so those other things can wait (even if you have a significant other who doesn't think so) because he needs you more now then those things need to get done right away.