If you are going to seed, do it the last two weeks of August. Otherwise, just sod it, water initially, every day for the next 7 days, every other day for the next 7 days, then every 3 days for the next 7 days. (At least two inches of water per application) The sod farmers have access to seed and chemicals that the common homeowner simply can't get.
Source: have played in the dirt professionally for over 30 years.