I have a coworker who is currently studying for the Professional Engineer (PE) exam.  Every morning I walk in to work and find him studying.  He has been very focused and diligent in his preparation, and I have no doubt he will pass the exam.  Watching him brings back memories of studying I have done when preparing for the CHFM exam.  Seeing him jump in enthusiastically at first, then as time and study fatigue have set in, he’s gotten to the point where studying is not so much anticipated and enjoyed, but rather endured.  Now the end in sight is all that keeps him engaged in studying.  It’s why many of us after walking out of an exam say “I’m never going to take that exam again!” 

I’ve been thinking about the preferred timelines when studying for a professional certification.  There is definitely a sweet spot to begin that isn’t too far ahead of the exam, but not too late either.  Beginning too early, you lose focus and drive, resulting in not being prepared when the examination day arrives.  Beginning too late, and you risk not truly learning the material. I think the ideal timeline is below.
Greater than 6 months out- work and get experience in the field of study.  This is generally where you are presently at.  Become aware that the certification exists and is attainable and relevant to your career path. 
4-6 months out- determine that you actually want to begin studying for the certification. Search out others who have the certification and speak with them about their experiences.  While it’s unethical to ask for questions on the test, they can direct you to study materials they used and found helpful.  Collect study materials and begin studying.  Check on exam registration dates.  Some exams are only offered at limited times during the year.  If your exam is like this, take note of the booking window and plan accordingly.
2 months out- book the exam.  This will help lock you in and help you remain focused.  You now have a deadline to work toward.  
6 weeks out-  take practice exams.  This will help your confidence in testing situations, and will also help with recall.  Practice exams also help direct you to weaknesses in your knowledge so you can go back and study those areas.
1 week out- you should feel reasonably confident in your readiness.  Review all of the material at a high level, then at a deeper level of anything that you feel needs final polishing.  If there are any equations or calculations, take special note to understand each one and its application.  Continue taking practice exams.
1 day before- let up on your studying.  If you don’t know it by now, any studying you do will be too late.  Rather than study, take the time to relax and get in a good mental state.  This will help you more than cramming.
The day of the exam- lightly review your notes and major topics.  Plan to be at the testing center 30-45 minutes early.  This will allow you to not be stressed if traffic is bad.  Take a snack with you and enjoy the snack before you go in for the exam.  Any time you have after arriving but before the exam starts gives you one final opportunity to brush up and confirm that you know your stuff.  Walk in and be there five minutes early.  Sit down and enjoy your exam.  You’ve worked hard and you know your stuff!