Yes, you are right, yet I might have put them in by 5-15, and the deluge of 5-23 would have decimated many. Best to grow more in cups, wait to 5-30.
Meanwhile, what think ye of this? There is a tall maple tree on the East side the building in which we life, and with an area of bare ground spotty grass and weeds under it. LL lets me manage it, and I bought some perennial rye grass, and did some soil clean up and prep, and I do not remember seeing any Maple seed "helicopters."
However, after two days I found quite a few. And which is what happened a few years ago when cleared, dug up the whole area so that it was bare ground. The tree really rained down its seeds.
I read that Maple tree seeds fall from late summer to early fall, but IIRC in the previous case it was also early summer. I actually suspect that the tree can sense when the ground is ripe for growing.
Interesting about the Maple but I don’t know anything about them.
The repotting I mentioned was that when your seedlings have matured enough that it is time for a larger pot, then repot them into a larger pot while still inside the house, don’t put them in the ground outside until the second growth is full and ready.