I got this info from this site. Hope it helps...

water 15-20 minutes twice a day for two weeks
water 20-30 minutes once a day for one week
water 30-45 minutes once a day every other day for one week
water 30-45 minutes once a day twice a week for one week
move into deep irrigation, increasing the time to provide 1 inch of water all over and decreasing the frequency to just once a week.

Starting off, the schedule supplies roughly 1/4 inch of water, then increases that amount while decreasing frequency of application at the same time. Like practically everything that concerns lawn care, this schedule is a general guideline and should be modified to accommodate your specific conditions. The lengths of time should be modified if you have an automatic sprinkler system since that will not take as long to provide adequate moisture. So, decrease amount of water (time) but maintain frequency as is. The tuna cans test is recommended. If it is still especially warm, you may want to irrigate 3 times a day (10-15 minutes if necessary) for that first couple weeks. Your objective is to keep the upper 1 inch of soil moist and not let the seeds dry out.

Thank you - however, these are the guidelines for a newly seeded lawn. As I described in my original question, I just overseeded an existing lawn.

Joel

I'm following this on my overseeded lawn and it seems to be working great.

jweiner,

It doesn't matter. The water is to get the seeds to germinate. The seeds need the water regardless if it is an existing lawn or a new one. (Your problem, of course, is that the existing lawn will grow like crazy because of the water). But the seeds need the water to grow. Otherwise, your germination rates will be lower and some of the seeds you spread will go to waste

You need the seeds to germinate, that's the number one priority. So for a short time, the watering schedule won't be ideal for the established lawn. That's OK, the lawn can take it. If you don't baby those seeds along, they will die.