kkay, does your flavor/vapor seem lessened? If so, that's probably time to change the coil. Everyone gets different life from a coil. Mine might be able to last a couple of days or even up to a week. Depends on the juice you're vaping and how frequently (and how high volts/watts you're hitting.) If I remember, you're about 8-9 watts (which is not overly high) I usually go by the flavor or tightness of the draw. I noticed it the other day with one tank I was using. Just seemed tight and the flavor was meh.
Sure enough (it's one of my kangers that I rebuild) the coils were coated with residue and the wick was filthy. Changed it out, and voila, I was back in flavortown