i think not showing up is one of the quickest things they will fire you for. and i dont see how they need to ca for it either, if they are missing that much that they are not even available to ca. i know 3 straight is job abandonment.
they basically tend to give new people (say between 90 days and two years) a ton of leash though. probably in a desperate attempt to increase retention. after a few years and proving you are reliable you will be graded much much more harshly. at that point you will be allowed maybe 2-3 incidents in 6 months. unless you are a favored one.