This link is for sod. I am doing it the old fashioned way with topsoil and seed...According to Scott's it's twice a day:
How Much Do I Need to Water My New Grass?
Watering is crucial for seeding success. Water twice daily (or more if conditions are extremely hot/dry) to ensure the top 1 inch of soil stays moist. Continue watering daily until you have mowed the new grass 1-2 times. Once your new grass is established, you can go back to a normal watering routine.