This is my first year winter sowing too, so hopefully someone with greater knowledge will chime in. Just for the record, I winter sowed a few perennials too soon, back on December 13. I used recycled salad tins with clear plastic lids. I made slits in tops and bottoms, added soil & WS my seeds. I figured they would never sprout since I started them so early. They froze solid but along about the 3rd week of February they thawed. There's A LOT of condensation inside all of them. Yesterday I took the lid off one--I was going to lift out the soil and place it in a milk jug. Guess what? It was FULL of SPROUTS!!! So I put the lid back on and set it on the ground right where it had been all winter. It's Chinese globeflower. I also have sprouts of lupine, bachelor button, anise hyssop, poppy and candytuft.
My guess is your containers of tomato seeds will be fine. With longer hours of daylight plus warmer temps ahead they'll begin to dry out naturally.

Poke a hole in the side of the container, near the base. Use a steak knife, stab it in, and give a twist.

T

I thought condensation is normal especially since I have plenty of drainage holes.

Later on when it gets warmer, it may not be such a good thing.

It shouldn't hurt your sprouts as long as you have drainage and aren't holding water in the cups themselves. (no standing water I mean.) Condensation is normal and a good sign that things are good and moist for the seeds. Once you get sprouts you can widen the air holes and after true leaves get rid of the tops.

Thanks everyone!

Christine

So, after true leaves - completely remove the tops? I was wondering about that....Thanks, flood

EG