How to winter sow seed that need light to germinate.

I thought that winter sowing began after freezing weather (we are in zone 4/5) has put all deciduous plants into dormancy. (Not true?).
We would like to sow Astilbe chinensis 'Pumila' seeds that need light to germinate.
Do we just put our jug with moistened peat/perlite outside in January with the top off? How long before it needs to be closed?
I'm trying to not overthink this but I didn't make it.

Maybe it just as simple as sewing the seeds on top, closing the jug and waiting for spring.

Al, that's exactly how easy it is...You dont bury the seeds(so fill your WS container and then put the seeds on top and lightly push into the soil) because they need the light to germinate, but they will germinate at the right time. You should do your wintersowing anytime after the winter solstice (December 22?) You put the closed jug out...do not leave open

Good luck...feel free to ask any other questions!

I'm overthinking things again:

In nature all seeds fall to the ground. Many seeds need to be covered when sown in the spring but are the rules different for winter sowing in that ALL varieties of seed should be sown on top of the growing media and just pressed in?

Mine I put out with the cap off, so a bit of water washes through, but they get some air and light too and yet are protected. You can do it earlier than January, some people do it in Dec or even earlier. I do put a bit of the "soil" on top, I usually just do it the usual way (big seeds covered more than tiny seeds).
Then in spring, gradually take the top off.