Depending on which role you're being promoted from, it may take up to two weeks. I forget how many hours is necessary for training. If you're great at multi-tasking, then it shouldn't take you very long.
When I was promoted to GSA (this was in 2008), I was only given three days of training. But I was also doing GSTL shifts technically before the promotion, so there wasn't much for me to learn that I already didn't know. If you're new to cashiering and the service desk, then they will give you training in those areas first. Probably a day each that area. They may also introduce you to the cash office and how all that works if they want to go the extra mile.
Ah, a week should be more than enough for you both then. It's not an incredibly hard position. As long as you're not shy with using the walkie, a strong pusher for red cards, and great with keeping guests first, you should do great.
Depends if you already coming from the front end and how much cross training that want you to have for all areas.
They may want you to be checked off for cashier, Service Desk, cash office, carts, and Food Ave/StarBucks. If you have prior experience on the front end, you may skip right to the core GSA duties and cash office.
Weeks?! Weeks?! They threw a fit when I got ticked off that my main day of training (4 hours) turned into covering guest services because the GSTL called out. They told me I would be fine and I already knew how to do it. Umm...I've since mostly figured it out on the two hours I got the next morning from a GSA, but I know there is a lot I don't know. So I hope you get more training than I did!