Most people get their Stipend within a couple of days of starting their Gold Membership. Keep in mind that it goes directly to your Zen balance in the C-Store. It does not show-up on your Account. The only way to see it is by accessing the C-Store in-game or on the website and seeing a 500 Zen increase in your available balance.

If you do not have that increase you need to file a Support Ticket. Posting on the forum will not do you any good.