Mike, I don't typically worry about it too much. I harden off in the shade the first day then move them further into the sun and wind for a few more days, rotating the flat as I bring them in and out. Tighter spacing may actually help them shade each other and support each other in the wind. Just a thought.
I only harden for a few days (3-5)then transplant into the garden with some protection. I figure this way they can harden while setting roots.
Someone I work with doesn't harden at all, straight from the house to the garden under protection. I'm a little skeptical about that.

Maybe when you are ready to leave them out all night you can take them out of the tote and separate them to expose the lower leaves to the wind and sun for a few days. Even if you can't do that, i think you'll be fine, especially if you're burying a good part of the stem at planting time anyway.

I think a week or so of crowding will give you leggy or at least tall thin seedlings. Some of the smaller ones may even suffer, while others will try to outreach their next competitors. I'm using 3.5" pots (about 12-13oz I think for the deep pots), 18 per tray, and they even look too close.