Tomorrow (Wednesday) is the last day immigration is open this week. Make sure you go early if you need something before next week, it'll probably be busy tomorrow.
It will DEFINITELY be busy next Monday.
TLDR : Answer Summary
The post emphasizes the importance of visiting the immigration office in Thailand early, especially since tomorrow is the last day it's open this week, and it will be busy next Monday. A commenter reminds others that the office closes for lunch from noon to 1pm, while another inquires if this information pertains to all immigration branches or specifically to Bangkok.