Wilting... due to fertilizer, hardening, or what?

[cythaenopsis]

So I transplanted a bunch of seedlings to 4" pots. I used potting mix and blending in some fertilizer targeted for tomatoes, some stuff I used last year with some success. I've been putting the pots outside for a good 5~6 hours when the temps are above 60F.

Almost half of them have suffered some wilting, a couple more severe than the others. The stems are fairly firm and straight, but the leaves were drooping over like resting palm trees. The others seem to be doing well and the leaves are showing signs of enlarging, the stems beginning to thicken.

I was worried that maybe I was watering them too much. I'm using a condiment style bottle to deliver water close to the stem so I am not soaking the entire soil base. I've done this about 3~4 times per day. It doesn't look to be "damp off".

Is it possible the fertilizer is too strong for some of the seedlings? Should I shorten the hardening time outside?

OTOH, I have some seedlings still in their trays nestled in soil-less seedling mix, which I also put outside and they didn't show any sign of wilting at all.