That depends on many factors. Sometimes the item itself is defective and will crap out early. If the user doesn't top off the cart often enough, the atty will burn hotter and crap out early. If the user doesn't drain the atty at night, it can gunk up and crap out early.
Myself, I get a week or two out of an atty, seldom longer. I vape heavily, but drain at night and top off frequently. YMMV
My RN4081's go for at least a month or longer, with heavy vaping. I don't do a thing to them. At night it goes in a drawer so the cat dosen't get it, and in the morning I just start vaping.