The registrar change request is made by the new registrar. It is the auth-code given by the holder to the incoming registrar that validates this request.
The outgoing registrar receives a registrar change notification:
If the outgoing registrar accepts within 8 days, the registrar change is immediately validated.
If the outgoing registrar refuses within 8 days, the total duration of the registrar change operation is extended to 22 days before validation. The outgoing registrar may still accept the transfer before the 22 days.
If the outgoing registrar does not react within 8 days, the registrar change is immediately validated at the end of the 8 days.
The transfer operation is billed and changes the expiration date of the domain name. The lifetime starts from beginning.
Trade and transfer at the same time are NOT possible anymore since 2015/06/30