Hours 0–6: Find out the reason. Call your broker or customs. The reason must be stated in the inspection report or notice. Without it you are shooting in the dark.
Hours 6–24: Gather the documents. If the reason is the documents, prepare explanations and additional papers. If it is classification, prepare the technical description and analogues. If it is valuation, prepare a justification of the price.
Day 2: Submit a written request. Ask for an informal resolution or provide explanations before a formal check begins. Often the issue is closed at this stage.
Day 3: Assess the risks. If the cargo is perishable, request expedited clearance or transit to a warehouse with the appropriate regime. Every day of downtime = money.
After 72 hours: If the issue has not been resolved, prepare a complaint or a court claim. Do not wait for the final customs decision if you see that the process is being dragged out without grounds.