5 CFR §839.612

1. (a)If you are an employee, your employer can waive the time limit for making an election if you request such a waiver in writing. The employer would have to determine that you exercised due diligence, but could not make an election within the time limit because of circumstances beyond your control.
2. (b)Your employer's decision not to waive the time limit under this section must be in writing and include notice of your right to request OPM to reconsider the decision.
3. (c)OPM can waive the time limit for separated employees, retirees, and survivors who exercised due diligence but could not make an election because of circumstances beyond their control if a request is submitted to OPM, and OPM concludes that a waiver is justified.