I'm not one of the experts on here but I would think the mower would blow your seeds and it would be counterproductive to establishing good soil contact. If I were you, I'd wait until your new grass is rooted.

I agree, leave it alone. There is a trade-off when overseeding into an existing lawn. Some sprout and you lose some. Mow when the new grass is 3 inches high.

In the larger bare spots (appx. 4 sq. ft.) some of the new grass is just under 2" tall, some of it has just started poking up through the dirt, and some of it is inbetween.

Which of these should be 3" tall when I mow? I can't really tell how tall the stuff within the existing lawn is. The existing lawn is at least 5" tall now.

Mow the tall grass and avoid the areas where the new grass predominates. When it gets to 3 inches, mow it back to 2. The tightrope you are walking is to avoid breaking the new grass (under 1 inch) and still allow enough sunlight down into the new grass so it will take root.

Thanks for the help. I mowed to just under 4" and maybe the grass wasn't quite as tall as I thought in most spots. Sometimes I felt like nothing was getting cut, but some of it was easily 6"+. The grass felt super plush when I walked on it, so I'm hoping I didn't do too much damage because I would love to keep it like that.

I've watered lightly twice a day for the last two weeks and decided to back off to a slightly heavier watering once a day now that it looks like most of the grass that sprouted is at least 1". When should I stop doing that and start the "deep and infrequent" watering again? After the first mowing of the new stuff?