How long will US Customs hold my package?

I had an aluminum drum (musical instrument) shipped to me from Cairo. It is my understanding that it cleared Egyptian Customs before it left. USPS tracking service has it listed as being in Inbound Customs now for 3 days. Is this normal? It seems to me that if they were worried about the contents because of the current revolution in Egypt, they could just open the package and see that it's exactly what the shipper declared. Anybody have any ideas how long this might take? Priority Mail -Hah!