FYI.
The wife and I have just been to Samut Prakan immigration to register the TM30.
Took all of 15mins.
I arrived on Friday, no fine was given for the late show up. Those worrying about arriving over the weekend shouldn’t.
However all the immigration offices are different I can only vouch for the one I attended.
TLDR : Answer Summary
The user shared their experience of registering the TM30 at the Samut Prakan immigration office, noting that the process took only 15 minutes. They mentioned that arriving late did not result in a fine. They advised that experiences may vary by immigration office.