I always apply about 5 weeks before my marriage visa expires and the stamp to report back is always dated the last week of my current visa, lady from immigration rings on the monday and we head over to get passport stamped next day.
Why don't you just visit immigration and ask them the question, take a person with you if not a Thai speaker. Most advice on this site is good, but why don't people ask Thai immigration, I find them pretty good.
just general question why is it such.a long wait for a Non O extension thru marriage, they (immigration) already say no visit to resident required, all other paperwork as required supplied, but always a 4-5 week wait. Plus I've also paid the required tax to Revenue, although that maybe a mistake as many not even registered meaning 180 day people.