Ask Mr. Smarty Plants

According to our Native Plant Database Muhlenbergia capillaris (Gulf muhly):

"Seed Collection: Collect seed in November when they start to lose the pink color. Use a comb so as to not damage the appearance of plants."

Since the seeds aren't generally ripe until November, it certainlly isn't too late to plant them in October.  In fact you want to be sure that the seeds you have (if you collected them from native plants) are mature.  Although you could plant in late fall/early winter (the time the seeds are naturally distributed), you could also wait until late spring to sow since gulf muhly is a warm season grass (WSG).  Here are the pros and cons from Stock Seed Farm about whether to plant in the late fall or in spring. 

"Dormant seeding in late fall offers natural stratification in the soil over winter and also reduces spring workload. This method often fails, however, because of weed competition during early spring. Late spring/early summer planting allows weed problems to be eliminated prior to planting, leading to more successful seedings. Weedy perennials can be eradicated in the fall, but any seeds in the ground will germinate in the spring. In most cases, a late spring planting is recommended for WSGs."

You can read more about gulf muhly from the USDA Natural Resources Conservations Service.