Ebay auto reminder on day 2. Day 3 send invoice with tactful enquiry asking for details of their payemnt as I cannot trace it. Day 4 open unpaid item dispute.

You can allow them longer if you wish but in my many years of selling I have found that if they are going to pay it is at the very latest when you open a dispute so waiting achieves nthing more than extending the time before you can SCO or relist.

There is no etiquette involved, it is a business transaction!