I have found through selling on eBay and also OZtion that buyers are often use to making payment within 7days which means they don't always contact you by your nominated day for example 3 days as your or even longer like 5 days, to let you know what payment method they are going to make !!

If you have recently sent them a message ... i would wait until about 7 days after them winning then send them a payment reminder .. thought that depends on when you mentioned in your selling when your payment duration is ?? ... Is your nominated contact 3days and/or payment 3days ??