Question
Hi my lawn knight in shining armor!  Do you remember me?  How was your summer?  

I was the person who lost 40% of my newly seeded lawn to a fungus because our gardener placed our topsoil directly on our clay soil and didn't mix them together at all, so the water just sat between the layers.  Well, to give you an update, I got a lot of weeds in the spaces but I hand picked them throughout the entire lawn. Now it's September and we seeded yesterday.  My question is this:  How often and for how long should I put the sprinkers on?  I don't want the same problem again!  Any advice?  

Answer
How nice to hear from you again.  I have been wondering how things went with that whole moisture situation.

It is not normally the time of year to do automatic sprinkling, but for new seed, you have to make sure there is constant moisture.  After all that work with the weeds - which I trust you did not let go to seed and faithfully removed - this is critical.  Twice a day, very very lightly, would be enough in this weather.  If it rains, turn it off.  If it's cold, touch the soil to see if it needs watering.  

There are products that can be purchased to retain surface moisture specifically for this purpose - I forget the product I have used, but it looks like little green hamster food in a hand held container, you just sprinkle it on by hand over the seeded area (in your situation maybe this is not so practical).  

Burlap is also helpful to keep the birds from eating the seed for breakfast.

Whatever you decide, just keep the seed moist.  It is so important to get this right.  And the absolute perfect time of year to be doing it.

Did you amend or rototill the soil at all before seeding?