In a typical transition from midwinter to early spring, I'd say frost seed anytime between the beginning of February and early March. Natural seeding knows no timing! The seed falls to the ground when it's ready. Then it waits for the right conditions to germinate. The good and the bad thing about clover seed it it has a VERY hard seed coat. So hard, that commercially processed seed is scarified in the cleaning process. That just means the seed coat is nicked, scratched, or broken (it's not a very precise process) so that some of it germinates after you buy it! Without out this, some clovers will sit in the ground for months and/or years.
Point being, it takes a while for Mother Nature to get the seed ready to grow. Freezing and thawing not only produces action to get the seed into the soil, it also is responsible for doing some coat cracking. This cracking will allow moisture to get to the germplasm and that's what starts the process. If you look at your seed tag, you'll see that a percentage of seed is hard seed. That stuff will lay in the ground a long time before it even thinks of growing.
But, the risk I think all of you have identified. If the clover germinates, the conditions for growth had better remain favorable. There's no going back! A seedling has a short root and if the soil around the root freezes for a long time (I don't know what I mean by that. There is science for it). it will die of thirst.
I talk a lot about philosophy. Mine here is, "seed in a bag isn't doing anybody or anything any good!" Strike when you can!
