Hi, my action is usually as follows -

Ebay send an automatic reminder 2 days after purchase.

An unpaid item case can be opened 4 days after sale date.

I usually send a message at 5 days asking if there is a problem with payment.

If no response, I open an Unpaid Item Case and that can sometimes spur a response or payment.
If not, I close the case as soon as I can, 4 days after it's opened.
Final fees are returned, buyer gets a strike, I add them to my Block Bidders List and re-list the item.

To open a case, select resolve a problem to the right of the item in the small drop down menu.