If it is a small package/parcel (i.e. not a big box like a kit), my experience is that it will sit in customs for 4-7 days and then it will probably go to your local Parcelforce depot. They will then send you a bill for the VAT/PO charges. When that is paid your package will be delivered (you can pay the bill at the Parcelforce depot if you want to save a bit of time).

If the estimate of the 10th came from the person who sent the package then ignore it. That tends to assume that the package goes straight through customs and they never do.