As a matter of advantage there is no limit prescribed to IMG to take the exam, one is free to take the exam anytime. But there is certainly a minimum time limit which is laid which is completion of second year. One has to wait until the completion of the second year of year to write the exam. Although there is no limit given Practically speaking if you are in a position to write your step 1 in IIIrd minor and aim to write your step 2 ck followed by CS during the internship year, this will surely help you save your academic years. If you do not follow be prepared to sacrifice your academic years and invite that grey patch on your CV.
This may or may not be possible, but if you try to aim for it and to a larger extent make it possible, things would surely be in your favour.
Abhishek Bavadhankar, USMLE & Residency Expert for over 10 years
Source: Quora Digest