After further research, the answer was in the Application booklet.
On page three it says "The oral examination must be taken within 3 years of the date of the initial notification of eligibility to enter the certification examination process."
So, the final answer is that if you delay taking the oral exam so that it occurs three years after the initial letter you received, declaring you to be eligible to take the written exam, you will not be allowed to take the oral and will have to start the whole process over (from scratch).
So, I would not delay in taking the oral.
contact me if you want some suggestions. frpainter at gmail.com