It's highly unlikely that drinking baking soda will have any implication on the results of a drugs test. Therefore, it wouldn't make a difference how long you wait before you have a drugs test after consuming baking soda.
There is no correlation between the two other than the myth that surrounds them. Drug users become desperate when they are required to take a drugs test, and will try almost anything to trick the test.
In reality, the process of eliminating drugs from the body is a lot more complicated than cleaning out some pipes with baking soda. Not to mention the fact that it can be highly dangerous, and there have been cases of people drinking huge amounts of baking soda, and ultimately losing their life.
How can you pass a drugs test?
The only method that's 100% guaranteed to help you pass a drugs test is to not take the drugs in the first place. Other than that, it's a waiting game, and usually takes a lot longer than a few days or weeks to be completely free from drug traces.