There is a certainly kind of earnest curiosity, in your questions. I guess, a lot of people on this forum (including me, sometimes), believe that they are too elementary, at times, but, please don't let it bother you.
I have worked in a few features, and we had a DoP/ Cinematographer, with about 30 years of experience (or more), who, more than once, missed shadows, and bills on trees, in the frame. Though, he was broad-shouldered enough to admit his folly, the moral of the story is, no one is perfect :)
The length of the time left, on the card, depending on the MB rate, you are shooting at.