Replying to Kid on ebay

So I sold a pair of eg1 or 5 idk what they were but they were the rasta pinstripe ones on ebay to a kid. Idk if hes on here or not but if you are pm me. He paid on the 8th but a family member had a stroke so i could not send them out till like the 12th. I emailed im sayig they have been shipped USPS first class but they could have been sent out pirority(sp?). We have been exchanging emails a few times because he has yet to recieve them. On the 23 yesterday he write me saying he should have them by now( He lives in CA and I live in NY, totally across the country.) and he thinks i scamed him. Now I have a recipt with his name, package id#, and the date it was sent for proof and i said i could take a pic of it before and he said not to worry about it. Now im worried he is going to file a paypal claim only after awiting 10 days. When i bought Skis off on Malone it took 3 weeks from when he shipped. How long does it normally talk to ship USPS across the country?