It's pretty normal for things to grow much more slowly in the winter. At any given temperature, plant growth rates are pretty much correlated in a linear fashion to the amount of ambient light available -- the more footcandle-hours of light (intensity x duration) the more growth. In the winter, there is much less light available than in summer. I was taught that, for example, there are 85% more fch of sunlight available at the 42nd parallel on a heavily overcast June day than on a bright and sunny December day. This is due both to the shorter day length, and to the much lower angle of the sun in the sky, resulting in light rays hitting the surface of the earth at a much more oblique angle. This effect would be increased as you go north to some extent, and decreased as you go south, changing with the latitude as daylength and the sun's angle to the horizon change, but it's still valid even in Texas. Days to maturity are usually based on a spring/summer cropping scheme, unless its something which is specifically grown as an overwintered crop, like some of the British cultivars of sprouting broccolis.

That looks more like a water problem to me. You have a tiny seedling in a biggish pot. I'd go drier still, stop touching the leaves, and put the seedlings back close to the lights, almost touching.

An ironic advantage of living in Saskatchewan at this time of year is that we are north of all the storm systems, in the influence of the cool, dry air the first half of spring. Great for growing spinach and brassicas in tunnels. In mid-May, the jet stream lifts north and we get May gloom and even June gloom while all you northern U.S people get warmth and sunshine. Nothing more depressing than a 48-degree rainy afternoon in June amidst the futile realization that the sun is near the strongest it can be and isn't doing much.

Didn't mean to post this here. Low tunnels do rock for starting plants early.