Hello. Thank you for reaching out in Communities! It's a great way to network with other oncology nurses.
You asked how soon you can retest if you do not pass the OCN© examination. You have a 90-day eligibility period during which you are eligible to take the examination. Candidates may not take the same certification test more than one time during the 90-day eligibility period. For example, if your 90-day window was July 1-October 2, and you took the exam today, you would not be eligible to re-apply until October 3.
I would encourage you to look through the ONCC website at www.oncc.org for helpful tips on preparing for the certification exam. The test content outlines as well as the list of references are available for all certification exams. It sounds like you are already familiar with the practice tests. ONCC practice tests provide examples of the types of items you can expect to find on an examination.