I've used it for 2-2.5 hours max per day untill lvl 96, wouldnt really risk doing more since stun alch is pretty click intensive and boring and someone playing legit wouldnt last long doing that. You could try doing more but ive been pretty succesful this way, no ban and been doing it from like lvl 75 or so (curse alch). Also, make you sure you find a anomynous place where no one will run into you stun alching and report you or w/e.
Do you have lunar magicks? You could do the tan hide spell or spin flax spell, both make money and with spin flax spell you also get crafting xp. Its less xp than stun alcing but at least you dont lose money.