To clean and deodorize your carpet with baking soda you should really leave the baking soda on the carpet for 24 hours minimum.
Although you can just leave the baking soda on the carpet for a few hours but overnight or 24 hours is the best amount of time to leave the baking soda on the carpet before vacuuming the baking soda off the carpet.
Before you apply the baking soda to the carpet it's best to run the vacuum cleaner over the carpet to remove most of the dirt.
Then sprinkle the baking soda all over the carpet and let it sit for as long as possible but overnight is best or 24 hours.
The longer the baking soda sits on the carpet the more odors that the baking soda will absorb from the carpet.
Then I would use a carpet shampooer to shampoo the carpet to clean up any other dirt and odors that may be in the carpet.