You would need to have finished step 1 and 2ck by mid august to have the results in time for mid Sept, however taking the cs in June may mean that you wont get the results of that back in time to get your ECFMG certification before applications start around Sept 15th.
The worst possible scenario would be to rush through the steps and still not get certified by the start of application season.
Doing all steps in 5 months might be hard seeing as you are a long way out from basic sciences having graduated in 2011. Most IMGs take at least this time for step 1 alone. That said, it wouldnt be impossible to do step 1 in say 3.5 months and step 2ck in 1.5 months...half the prep for ck is in step 1. You would need to work your ass off though.
If you were considering doing it, definitely take an NBME exam for step 1 now, to see were you stand. If you get a poor score, then its probably not worth the risk rushing to take the exam and risking ending up with a below average score.
Getting poor scores or even a failure on your steps is likely to harm your application much more than putting off applying till next year round. You can always spend the year building your CV in other areas if you have more time than you need.