Root crops in winter greenhouse - does day length matter?

We have a mildly heated greenhouse here in the PNW of the US and I'm wondering if it's possible to grow some short season root crops, like baby turnips, in the winter. We get less than 9 hours of daylight right now and I'm curious if this will impact bulb formation.

Johnny's winter growng guide suggests that plants need at least 10 hours of daylight to grow well, so you'll probably struggle slightly I suppose, even with some heat. You might have better success with leaf crops like lettuce and oriental greens that cope with a bit of shade. Or leave sowing until the day length starts to get longer again.
You could do an experiment and sow some now and some in a month's time and see what happens.

I do have greens (spinach, microgreens, beet greens), along with my citrus plants (I keep one part above freezing at all times), peppers still alive from the summer, and a few other things. But for some reason I’ve been thinking my root crops won’t do well. I have some extra lights for peppers but I’m not sure I have room for root crops under them.

I guess I’ll experiment with a handful of seeds and see what happens. I was just thinking they may be like onions and form their storage organ based on day length.

If the light is bright the short hours are not much of a problem for young plants that normally seed in fall and over winter or sprout as soil warms.  So planting now is the normal cycle for what you suggested.  The gradual increase of day length will stimulate storage root development instead of bolting to seed.  My potatoes are coming up now and will be harvested in March.