I am unfamiliar with when TRICARE enrollment is "brought up."
Assuming you are a retiree, your TRICARE options are shown at: Home | TRICARE <---LINK
Reference: Defense Enrollment Eligibility Reporting System | TRICARE <---LINK
You must be registered in the Defense Enrollment Eligibility Reporting System(DEERS) A database of information on uniformed services members (sponsors), U.S.-sponsored foreign military, DoD and uniformed services civilians, other personnel as directed by the DoD, and their family members. You need to register in DEERS to get TRICARE. (DEERS) to get your TRICARE benefit.
Hello, rookie here. However, I was told that the first day of retirement (assuming like Ron) you can go to your local deers office and enroll. Please anyone correct me if I am wrong, but I hope this helps.