For the Gold plan with 10GB anyday + 10GB weekend, if I subscribe to AnydayGB on the third week, do I still get extra 10GB weekend if I didn't use any for the previous weekend, or it's pro-rated, so I actually only get extra 5GB (quota for the remaining 2 weekends)?

I'm intending to use the AnydayGB as a backup in case I finish my data, instead of using it permanent as monthly subscription.