Specific timing of what month to use on our Social Security benefits application

Terry,
I’m not the person you spoke to on John Williams show Wednesday 7/12, but do have the same concern the caller did for the specific timing to start Social Security payments. You were going to contact Larry Kotlikoff for a definitive answer, but I haven’t seen the answer posted on your site yet. My wife’s FRA will be 9/4/23 and my 69th birthday will be 10/12/23. As SS payments are one month in arrears, what date do we use for a start payments date when we apply? For my wife, do we use September, as that is the month of her FRA, or August to start the collection in September? I’ll guess it’s September.

Jim