Answer:

By default, F5 certifications are valid for 2-years, and have an additional 30-day "grace period" for renewal. 

The "expire" date is the date a certification will no longer be valid and cannot be used to satisfy prerequisites, or to access any other benefits of being "certified".

The "final renew" date (typically 30-days after the expire date) is the last date you may renew a certification without penalty by retaking/passing the last exam you took to achieve the certification.

Example:

Let's say you achieve the F5-CA, BIG-IP on January 1st, 2020.  The certification expiration date would be January 1st, 2022 (2-years after achieving it), and the certification "final renew" date would be February 1st, 2022 (30-days after the expiration date).