Typically 3-5 days (of cumulative use) here.
That’s been my experience as well.
I guess I started “bumping up my timetable” (to change coils more frequently) about a year ago.
Where everyday mixes are concerned:
I used to try and “maximize” the length of time I could get out of a coil. It took almost a notice of “Wait a minute… What the hell’s going on with the flavor here?!” to get my attention. Then I’d really look closely at the coil and realize “Oh, this is WAY past due for a rebuild.”
Often, there would be up to a 16th of an inch (roughly 1mm) of gunk built up on the coil.
But over the course of continuing to try and dial-in (fine tune) an established recipe, I realized that the instant I could detect that I wasn’t getting all of the expected notes from a very familiar recipe, it’s time to change the coil and cotton.
Nowadays, when I sense notes not coming through, it’s often about the time that you’re no longer able to see bare metal (just a slight coating of the coil).
Even though the metal (316 SS in my case) does change color, there is a distinct difference (to me) between the metal being bare (and discolored), and the point when it becomes ‘coated’.
Hopefully folks new to vaping can follow what I’m trying to explain above.