It depends what kind of plant it is. If they are tender annuals, I'd say yes. If they are perennials, I'd say no.
WS isn't about coddling your plants. They are to be left out in the environment -just like in nature.

It depends :-)

There's no absolute right or wrong answer here. It can vary with
-duration (a few hours? or several days?)
-actual temp (30 degrees or 15 degrees?)
-type of plant (perennials can take more cold than tender annuals)

I've never lost perennials from cold, but I have lost annuals. So now I often give annuals extra protection which might be an extra sheet for a few hours of light frost. But I've also put tender annuals in my garage when the temp was supposed to be below 25 for several days.

And as gardeners, we all have our own tolerances.

Karen

What Karen said. Also, you certainly don't need to worry if you don't even have sprouts yet. In your zone, it should be cold enough to keep most seeds from germinating, so they're safe. It's also surprising how much protection the containers provide. And even tender annuals that are wintersown seem to have just a bit more cold tolerance than store bought plants. Try to relax. I promise you will have more sprouts than you know what to do with come spring.

Martha