Honestly, I bet it ships by the end of this week.
Based on the data I've collected, I think the majority of 42mm SGS (in the US) hit between XX:05/XX:06 and XX:10. (Accounting for the fact that most "hardcores" used the Apple Store App to place their order in the first 3 minutes, while the majority of others used the website, which didn't come up until almost 3 minutes after preorders opened, and assuming it took 2-3 minutes for those first website people to submit their orders.) I think by the end of this week, we will be up to the XX:07-XX:08 orders (at least), and will probably finish out the bulk of preorders by the middle of next week.
You should start seeing the times of preorders start to move a lot faster after this week. So, XX:11-XX:20 people, I think you ship next week, easy.