How the renewal cycle works
Your licence fee covers the period from the date of licensure until the last day of your birth month in the fourth calendar year following issuance. Across that period you need at least 24 hours of Commission-approved continuing education.
The birth-month detail matters more than it sounds. Renewal is not four years to the day from when you were licensed, so working it out from your licence date alone will give you the wrong month.
Do not save the hours for the last year
24 hours across 4 years is six hours a year, which is comfortable. The same 24 hours in the final quarter is a scramble, and it tends to mean picking whatever course has availability rather than whatever is useful.
Before you rely on any of this
Confirm your own dates and credited hours with GREC directly. Renewal requirements are the sort of rule that changes between cycles, and your record is the authority on what you have completed.