Had an ekg & radiology done. both tests came back great. doctor told me to stop herbal stimulants. how long will it take until palpitations go away?

It depends: It depends on what you took and how much. Not all herbal stimulants are the same. You also need to know that the company making them is ethical, because some may mix in pharmaceuticals or other impurities. Label designations of USP or GMP offer some help. Some mixtures i've seen from non-european countries, for instance, make it impossible to know contents. Care and due diligence are advised.