Hi,
I have the same situation... business trip the U.S., departing BKK mid next week, will stay in the U.S. for about a week. I got all my documents in order this week and applied for the Thai Pass 2 days ago. It was approved within 36 hours.
In my experience, the Thai Pass system works pretty well. Clear instructions and if you follow carefully it should be fine. I'm sure there are many edge cases that they haven't adapted to yet, but so far, I'm fine with it. I don't know this but I suspect they are processing applications based on planned arrival date. I also have a Thai vaccine certificate so I cropped and uploaded the QR code where they ask for it. The application says that helps speed it up.
Good luck!
