I have been once to Soi Suan Plu for getting some info about a tii-juu (or yellow tabian baan).

I remember there were different floors etc.

So where do I have to go to, when I want to apply for a One Year Permission to Stay (Extension of Stay based on Thai Wife)?

What Floor, what Room? - What time is usually the best?

Related to this request is the question: When can I apply for the Extension once I have entered Thailand with a Non-Immigrant O. Do I have to wait until 60 days of the 90 days permission are over? Can't I apply earlier?

Apply during the last 30 days of your permitted to stay. Suan Phlu now has a desk directly inside and to the left of the entry doors where you queue and present your case papers and obtain numbers and instructions on where to go. The one year extension of stay is just to the right of the desk in a new (several years ago) large room on the 1st (entry level) floor.