I can't speak from experience, but the admins have said this on the issue
Recently, Paypal has changed their check-out system and it takes especially on weekends a lot longer till they give our system the notification to pay out those reds you ordered.
When it takes 6 or even more hours, please send a mail including the paypal transaction ID to email@example.com and we'll take care of it.
In case you used a debit/prepaid card and paypal, it is possible that it takes up to 7 days before they have it verified and gives the 'go' to our system.
Please let me know in PM, if its not the case.