There's still a chance that they won't check the content, not all packages are screened. It may also depend from the size of the parcel and declared value.
Do you know if it usually takes awhile for an item to go through customs
The rule is, if your item is stopped in customs, it is up to 2-3 days and it should be released if not subject to duty. Otherwise, you should get a letter within 7 days, that the consignment is stopped by the customs with information where and what kind of documents to provide (generally information on the content and proof of payment).
So after couple of days you should call them and determine the so-called stock number of your shipment (numer magazynowy) and then find out whether the shipment is subject to duty or not.