"Inbound to Customs" What does this mean?

I've ordered something on eBay and its arrived here yesterday in the U.S at about 8:30 AM. I just checked the tracking status and it still says "Inbound to Customs" since yesterday. How long does this process take and how do I know if U.S Customs has seized the package or not? Please help, I'm getting a bit worried. How long should I wait for? Should I try giving USPS a call or the U.S Customs? Btw, the item is an airsoft gun but it has a painted orange tip on it and there are no trademarks on it. The gun is also made of hard plastic, if that helps