Giffgaff calculates and gives out payback statements in the first week of each month. Your monthly payback points will be displayed within the 'My Giffgaff' summary page, and you can see into further detail of the payback statement by selecting 'My Payback' link on the very same page.
You will also receive an email from Giffgaff, confirming the amount of payback points you have earned within the last month shortly after being displayed on the website.
Hope this answers your question!
also, by 'appear in your account' you might mean 'turned into credit on my account so i can spend it'...
Every 6 months you can claim your points as cash (via paypal) or as credit (straight to your giffgaff sim).
You'll be emailled before then and there'll be notices on the website telling you what you need to do, when.
As the others have said, your points get totted up every month, on the 5th of each month. You can then claim these in November and July (I think!)
Just a point of interest:
When you get your Payback, I would advise you have it paid to Paypal and then top-up your account from there.....assuming you can withdraw the money as I can. By doing that you can top-up in increments that suit your usage and avoid the possibility that you have topped up SO much (if you have your Payback directed to your credit on your mobile) that your credit lasts more than three months thereby losing your free GG to GG calls and texts.
Just a thought.