One of my auctions ended on 16th March and have had no contact from the buyer. How long should I wait before I start an unpaid dispute? The buyer also only has one feedback from Oct of last year. I have sent an invoice and think I'll send another reminder and give him 4 more days..that will have been 7 days, which is an acceptable amount of time for payment isn't it?

Some disputes can be reported immediately after the item closes, but most require a 7 day waiting period. You cannot report a dispute if more than 45 days have elapsed.