when's the latest i can take step2ck and still have it considered in my application? i need to improve from my step 1 score but am thinking i may need more time.

Well you can hold off your app till you get your scores in - this may delay the application. There is no deadline for CAS but you want to try to get your app in as soon as you can. OR you can send the app and then later send in the scores individually as they become available to programs - this takes more time and effort. There really is no latest as you can hold off sending your CAS application till late November even.