If I were you, to be sure, I'd send an email to "customerservice@gentlegiantstudios.com" right now, and let them know you just bought a Premier Guild membership, and want to preorder the SDCC Jumbo Blue Snaggletooth. And ask them to email you as soon as you are eligible to make that purchase as well.
Might not make any difference, but then again, it couldn't hurt either.
Also, I know I mentioned this before, but make sure you get that free one time promotional code (in email) to get your free gift for signing up. And one of those is the Jumbo Gamm. Guard.