It's usually instant, but if you don't receive it right away then you'd have to wait 5-10 minutes, but in this instance you said it's been 2 1/2 hours, so I'm assuming your donation is pending. It would be marked as pending in the donation center if this is the case, but if that's not the case either I suggest getting in contact with @Matthew to help fix your issue as he handles all donation related issues on Sythe.
Yeah then I'd recommend sending @Matthew a message on the forums, and having him help you with your situation. If you have any other questions regarding, then feel free to post below, or message me anytime, but contacting Matthew, and showing him proof of your donation, and explaining the issue that happened is most likely the best way to go about handling this situation as he's the head of all donations made on Sythe.