My biggest question with the second power raking is if you scattered the seed and may have heavy spots in some areas and still have bare spots that you are trying to correct in others.
That said, I probably would still have used some mulch straw- how much depends on how much other material you had after power raking. Did you remove the debris after the first power raking?
15 minutes doesn't tell me a lot. Depends on what kind of watering you are doing. Irrigation system, hose-end sprinkler, holding it by hand, etc.
The end is that you want the seed to stay damp. A little too much water would not be as great a problem as letting it dry out and die just after it sprouted. The worst is that you are wasting water and a utility bill. If I had it on a timer, I would go for 10:00, 2:00, and 6:00. And some will say that the last two will just evaporate. It will, just as it will evaporate from the seed.
If it's worth doing, it's worth doing right. If you wouldn't put your name on it, it ain't done right!