I know it has to be sown fresh, but how fresh? Is straight off the plant preferable or will a few months or so in a seed packet be OK?

I have some astrantia major plants which are seeding and a packet of 'Margery Fish' from a seed swap. I really love the dark coloured varieties and astrantia maxima and would like to try a couple of those as well.

I was intending to sow them in pots and leave them outside over winter in a sheltered spot. Is this a good idea? Are some varieties easier to germinate than others?
All comments gratefully appreciated.
Thanks

From that I'm supposing cool temperatures, free draining while still holding moisture, reliable water, and mild light rather than sprouting in the dark. Lightly covered.