I am assuming you do not over seed your yard in the fall/winter.
Source: http://www.turffiles.ncsu.edu/turfgrasses/bermudagrass/lawn-maintenance
For the Sep-Nov timeframe
"Apply no more than ½ pound of nitrogen per thousand square feet in September, four to six weeks before the first expected frost. Use a low-nitrogen, high-potassium fertilizer such as a 5-10-30, or supplement a nitrogen fertilizer source with 1 pound of potash(K2O) using 1.6 pounds of muriate of potash (0-0-60), 2 pounds of potassium sulfate (0-0-50), or 5 pounds of sul-po-mag (0-0-22) per thousand square feet."
Source: http://www.turffiles.ncsu.edu/turfgrasses/bermudagrass/lawn-maintenance
For the Sep-Nov timeframe
"Apply no more than ½ pound of nitrogen per thousand square feet in September, four to six weeks before the first expected frost. Use a low-nitrogen, high-potassium fertilizer such as a 5-10-30, or supplement a nitrogen fertilizer source with 1 pound of potash(K2O) using 1.6 pounds of muriate of potash (0-0-60), 2 pounds of potassium sulfate (0-0-50), or 5 pounds of sul-po-mag (0-0-22) per thousand square feet."
