shows you what you get when you sell/buy your cash to kasikorn, which will give you 329,451.60 baht right now for 10k USD. When sending money you get less.
The screenshot shows you what you get from wise right now.
I always do the extension in the last days. 2-3 days before the end is enough time to get all paperwork done. But lookout for Thai holidays - I have added the Thai holidays calendar to the calendar app for that. (Important notice: if a Thai holiday falls onto a weekend, the next workday is holiday!)