If you want to be fulltime, why are you asking how many days your allowed to miss? Thing happen, yes, but if your wondering how many days you can miss..... If your sick your sick, but then again, if your getting sick often you need to self reflect, unless its a non-controllable condition.
Every contract is different. In Seattle area you need to do 12 consecutive weeks at a full 40 then you can not drop below 36 hrs more than a few times before it'll drop your full time status. I've done this before and was classified as p.t. I think the managers have to change it in the computer system.