13 CFR 115.64: Timeliness requirement.

There must be no Execution or approval of a bond by a PSB Surety after commencement of work under a Contract unless the Surety obtains written approval from the D/SG. To apply for such approval, the Surety must submit a completed “Surety Bond Guarantee Agreement Addendum” (SBA Form 991), together with the evidence and certifications described in § 115.19(f)(1)(ii). For purposes of this section, work has commenced under a Contract when a Principal takes any action related to the contract or bond that would have exposed its Surety to liability under applicable law had a bond been Executed (or approved, if the Surety is legally bound by such approval) at the time.