The minimum has been reduced to two days, 48 hours.
However, I usually wait until Day Three has passed, send a polite reminder, then if there is no response open the Unpaid Item Dispute.
About half suddenly pay, apologize and leave positive feedback. The rest disappear with the Strike they just earned.
Keep cool. It's business not personal.
BTW, even when he does pay, as a new seller, Paypal will hold the payment against your good performance for 21 days. You still have to ship once PP has the payment.