You can of course keep trying Stadia support but from what I've seen on here and Reddit they will likely tell you it may take 3-5 business days and to contact them again if you still haven't received the code by the end of the week.
I checked my order and it is listed as "not shipped" yet it's been sitting here in the box for over a month. I was speaking with support (got a callback in about 45 min) and it seems the shipper did not get in good communication with the order department. At least that is the best I can figure out. I was told they are redoing the order/shipping process to find the errors for those who ordered Founder's Editions as I did but have not received their invitations as of November 20th. I did make the point that the "only" reason I ordered was the opportunity to acquire a unique name. That was the thing that moved me to purchase. Now that the good names are gone, I wonder how they are going to make that up to us?
Yesterday, 20 Nov. received notice the controller sitting here for a month was shipped. Progress! Then, tonight by 7:30 pm, I receive my invitation, registered my name and paused before starting free trial. Once burned, twice shy. I'm going to wait awhile and see what happens when the dust settles.
It's gut check time, Google. Let's see how you handle it.
Just got it in my inbox a few hours ago!
Just received my code 10:50pm. Pre-ordered 14th September and received product 9am yesterday