If it was parcel post (no tracking or ref number), that is all surface transport and can be as long as 3 weeks across country. The risky part about that is I'm convinced that's the service where airline baggage handlers get trained to destroy packages in new and creative ways, largely because that's how people seem to ship heavy things like pianos, rock collections and barbell sets by post, so your box is more likely to get things stacked on it. Keep your fingers crossed that the seller packaged it well.
Once it goes on beyond 3 weeks it might be time to have the seller put a trace on it. I once had a package end up in the dead package pile because some other package leaked and erased all the address info from the labels, they had no reason to look for its owner until the seller flagged it as missing in action.
