Late summer is the best time to establish Kentucky bluegrass, creeping bentgrass, tall fescue, and perennial ryegrass from seed. Between August 15 and September 15 is optimum seeding time in the northern half of Indiana, from September 1 to September 30 is optimum in the southern half of Indiana. It is critical to seed as early as possible within these windows. You likely cannot seed too early and even when seeding within these windows, waiting one week later to seed may mean the stand will take two to four additional weeks to mature. The primary reason that late-summer seeding is preferred is that it maximizes the time for the grass to establish before it faces the heat and stress of next summer. Even though a late-summer seeding requires frequent irrigation, limited weed and disease pressure, warm soils, and moderating air temperatures encourage quick establishment. More information can be found in AY3: Establishing Lawns From Seed at http://www.agry.purdue.edu/turf/pubs/ay-3.pdf