All depends on how you asked the seller to ship it and who he/she uses. Normally, USPS priority is the best service. You can ask the seller to mark it as a $40 total package cost and you will get it within 7 - 15 days excluding weekends. If it has not arrived by then, it will be held up in customs so expect a slip through your door to pay charges. Flat rate delivery charge from Parcel Farce is £8.00 plus whatever they feel like charging for the package.
Oh, double check too as sometimes Parcel Farce will send the slip to the wrong address. You wait ages and ages and then hear the parcel has been returned to the sender. It happened to me once and when I contacted Parcel Farce, they had sent the customs slip to a completely different address in the top half of the country even though my address was clearly visible on the parcel
If it was me Sam, I would wait another week and then contact Parcel farce mate