Probiotics are not an instant fix, they need to take root and grow before they can really get to work. This happens faster if you mind your diet and consume more fiber rich food and make sure to get enough sleep, as the microbiome follows the circadian rhythm. It also depends on whether you chose to reestablish your gut flora through a changed diet, or through dietary supplements. One can say that it generally takes 60 days to restore the microbiome through food, and around 30 days if that is combined with supplements.