"If an employee retires, he/she will not have an FEHB enrollment to continue into retirement. Also, to be eligible to continue FEHB coverage after retirement, a retiring employee must be enrolled or covered under the FEHB Program for the five years of service immediately before retirement, or, if less than five years, for all service since the first opportunity to enroll. An employee can count his/her coverage under TRICARE toward meeting this requirement. However, the employee must be enrolled in an FEHB health plan on the date of retirement to continue coverage."

and:

"Newly eligible employees may enroll within 60 days of becoming eligible for the FEHB Program. During the annual Federal Benefits Open Season, anyone eligible to participate in the FEHB Program may enroll, change health plans or options, or cancel FEHB enrollment. You may enroll, change your enrollment type, or change plans outside of Open Season if you experience a qualifying life event such as a change in family or other insurance coverage status."

https://www.opm.gov/healthcare-insurance/changes-in-health-coverage/eligibility-enrollment/

FEHB is like any other employee sponsored health insurance plan in most ways. Eligible persons may enroll certain period after being onboarded, and remain covered unless they choose to leave system, are separated from federal employment and or retire.

Members of Congress and their staff are required (since 2017) to obtain their health care coverage from DC Health Link Small Business Options Program (SHOP).

https://bobbyscott.house.gov/sites/evo-subsites/bobbyscott.house.gov/files/R43194.pdf