It's getting a little late to be starting seedlings in Zone 5. It'll take 10-14 days for them to germinate, and another month to reach any size, and by that time the monarchs will all be headed for Mexico.
However, the seeds you received are probably tropical milkweed, which can be wintered over indoors, if you have greenhouse conditions (meaning not just enough light but plenty of humidity).
The best course would be to put the seeds in the 'fridge until March, then plant them and put them in a sunny window, and by May (Monarch time), you'll have little plants you can set out.
I doubt you can do much with them yet this season, but feel free to try a few. For some reason, monarchs seem to love to lay eggs on tiny milkweed plants.