This will only get rid of surface stains on teeth there’s a big difference in getting whiter teeth from tooth stains and bleaching teeth if you do this too often you can damage your enamel if you want to bleach your teeth the only way to do that is using things like whitening strips. hydrogen peroxide is the only thing that will whiten teeth using acids and abrasive materials like the baking soda in this “hack” will only dissolve your enamel
wouldn't really matter anyways, it would take longer than just the first time doing it. twice a week and over a period of time you would notice if it does help.
