The next few weeks are the best time to seed or overseed.
Seedlings germinate quickly at this time of year due to (a):
-Residual summer soil warmth
-Moderate day temperatures
-Cool evening temperatures
-Consistent moisture (i.e. an increase in rainfall)
-Less active period for disease and weeds
Seeding now will encourage a strong, deep root system before the winter. This will promote strong spring growth to fend off weeds and summer stress more effectively!!