How long does it take to port my cell phone number from AT&T to Straight Talk?

I am looking at changing over to the TracPhone Straight Talk, which is sold at Wal-Mart. I currently use AT%26amp;T Wireless but am out of my contract and ready to switch due to the price difference and needs. I want to port my number from AT%26amp;T to Straight Talk... How long will it take them to port the number? I ask since I used to work for Time Warner Cable and it would take (if I recall correctly) a week to port it. I just need to know before I go buy the phone and then then shut off my AT%26amp;T! I don%26#039;t want to lose my number... Thanks for your help-|||I ported my number from t-mobile to Straight Talk it took a few hours.