19 CFR §182.46

1. (a)Time of filing. A drawback claim under this subpart must be filed within 5 years after the date of importation of the goods on which drawback is claimed. No extension will be granted unless it is established that a CBP official was responsible for the untimely filing. Drawback will be allowed only if the completed good is exported within 5 years after importation of the merchandise identified or designated to support the claim.
2. (b)Method of filing. A drawback claim must be filed electronically through a CBP-authorized electronic system (see § 190.51 of this chapter).