It took about six days for Samsung to credit my Fold 4 trade in from they day they received it. It took about nine days from receiving the Flip 4 trade in towards the Flip 5. I'd be chatting with Samsung past the ten day mark.
So mine was received at Samsung (or their 3rd party place) on the 29th of August. It still said pending receipt. They told me they were backlogged and to contact them after 10 business days if it had not been completed. Today it still said it so I contacted them and they manually completed the trade in. So finally after about a month of sending it, its completed.