As long as you don't use the label eBay charged you for, you will be refunded after it expires, probably is thirty days (although it will expire much sooner than that).
You may find you can not add your tracking details to the transaction, as eBay will assume you will use their label. Therefore, I imagine your payment will be treated as untracked, so your payment should be available 14 days after the date of the order. (If the item cost less than£10, you should be paid quicker if the buyer leaves positive feedback.)
