OK, it is actually much more simple than described above.
Step 1: FAA has a 30 day no questions asked return policy. So, 30 days after the sale the money has "cleared" and is yours.
Step 2: FAA pays every month on the 15th. (or the first business day after the 15th.) ALL cleared money is payed then.
For your calculations, if you were to sell something on the 16th of September it would clear on the 16th of October so would pay on the 15th of Nov which is about two months. Conversely, if you sold on the 14th of Sept, it would clear on the 14th of Oct which means you would would be paid on the 15th of October. So the quickest you could get paid is one month. The longest is two.