It's hard to know because I vape 3 or 4 different ones in the evening but... I'd say about 2ish days.  For morning and afternoon, I have two going that I swap between - banana nut bread and caramel cappuccino at 24 mg.  After dinner, I switch over to dessert and fruit types and those are mostly 18 mg with some 12's in there too.
I'd smoked about 2 PAD for 31 years and started vaping fulltime, no cigs, 1 month ago (on Monday). 
 I don't think what I'm vaping is excessive but even if it is, I don't care! LOL  I absolutely LOVE vaping.  At night, sitting on the back porch with the fireplace going, chain vaping strawberry shortcake, peaches and cream, key lime pie... pure nirvana. 
