When transfer occurs
Primary source
Verbatim text below is from the Electronic Code of Federal Regulations (eCFR), a public-domain U.S. government work. Always verify the current version with the eCFR before relying on it for any legal matter.
Full Text
(a) OPM, the Department of Defense, and the U.S. Coast Guard will transfer the amount specified in § 847.504 as soon as practicable after receipt of an election of retirement coverage under subpart D of this part.
(b) The transfer of contributions may not be delayed until the employee retires or separates from service.
This is legal information, not legal advice. Laws vary by jurisdiction and change frequently. Always verify current law with official sources and consult a licensed attorney in your jurisdiction for advice on your specific situation.