I would wait until early to late September but not after October 15th. Ohio summers can get pretty hot, especially in August, and if there's not steady enough, consistent rain, we experience drought conditions that can cause grass to enter dormancy. We've had June and July temperatures in the low to mid-90s this summer, so I think autumn planting is better for seedlings to develop strong grass blade roots. A long-term weather forecast may give you a better guesstimate on rainfall. Self-watering is OK as long as the seeds are monitored continuously.