Shelly,
Why not apply PMP to this situation?
Your Project: PMP Certification.
1. Evaluate if this a real problem or just a perceived problem.. Give some standard PMP tests e.g. PMStudy 1,2 and check the scores. If Scores are above 70%, you're fine. it's just a preceived problem, you can't be 100% ready anytime. There would be unknown-unknown risk always (though small in %age).
2. If scores are below the line (<70%), Check what options you have:
A. Is there any constraint that you have take test in few days ? (Schedule Constraint) or do you don't want to put extra money in rescheduling (Cost Constraint) or you're fed up with preparations and want to give asap (Constraint with Customer satisfaction)
B. If you're doing OK with the constraints, check what is the impact Postponing would have. When do you think you would be ready (Parametric estimate, per knowledge area : 2 days, e.g.) or analogues example (last time I finished entire Rita book in 10 days). Calculate the variance using Three Point Estimates / PERT. Add buffers to it (for contingency reserves) e.g. Office work didn't let you study for PMP for 2 days.
C. Then Re-evaluate, take standard exams and benchmark (70+%)