The buyer has 4 complete days to pay.
Although you have accepted an offer, the item remains for sale and you are free to accept a higher offer, or sell for the asking price, if the other buyer doesn't pay promptly.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)