@Ryland A few people have started similar thread here and on the Reddit sub. But it's clear one thing that there's really no pattern. All we know is that initially there was a bit of issue where codes were sent out of order, but now they're back on track to send them in order.
But if you still want to know, I ordered June 6th 9:26 AM Pacific - got my code Nov 19 12:59 PM Pacific.
Might want to take a look at this post as well:
https://community.stadia.com/t5/Stadia-General/Stadia-CodeHelper-code-help-proof/m-p/1712#M828