I'd say minimum 15 minutes, longer if you can keep everyone off the carpets for that long.
Arm and Hammer Carpet and Room Deodorizer is supposed to be good... I imagine it's mostly baking soda and probably doesn't cost a whole lot more than a couple of boxes of baking soda, so you might want to try that.
Do you have an exhaust fan in your bathroom or kitchen? You could try turning that on, and maybe setting up an oscillating fan in the other rooms to get the air circulating a bit more.
If you scroll to the bottom of this article there's a list of safe, natural, chemical-free suggestions for freshening up the air in your place:
http://www.eppa.ca/meetings/spring cleaning.html