For posted items I wait until day 3 then send an invoice asking for details of their payment as I cannot locate it and their item is packed and ready to send. If they don't pay by the end of day 4 I open the dispute. They still have another 4 days.

Completely different if it is a pick up item. I contact them straight away giving them my phone number and if I don't hear from them by day 3 I ring them. Pick up arrangements are much better handled on the phone and as my buyers can only pay with cash if they are picking up they cannot pay with Paypal to avoid an unpaid item strike and then chargeback later if they don't want to continue with the sale.