Wait until you can see the first true leaves between the two seed leaves.
Don't let them dry out, and thin seedlings when they form their first true leaves.
Now was that real and true leaf then and there destroyed?
Do this after they've developed a couple of "true leaves."
They use the sugars to keep true leaves growing.
Seedlings should have at least two pairs of true leaves before they are "pushed."
The first two leaves of any plant are not true leaves.
And when you are thinning seedlings, wait until a few true leaves grow.
Begging those first true leaves of the potted basil to come up.
While the ground is warming, they'll germinate and make their first true leaves.