Hopefully, your payout for the item is still within 48 hours of delivery. But if you're upgrading your postage method to Special Delivery you'll have to wait 14 days (possibly more) to have the SD label refunded to you and will have to make a claim from Ebay for this.

Various sellers have reported delays in this process and some are still awaiting refunds (possibly rejected?) from a few months ago. Ebay is not making this process as easy as it might be, but with SD in place they don't like sellers doing their 'own' thing. Even if the own thing is upgrading to a better service.