You can certainly do it. I have scattered seed around outside from early spring to late spring (sometimes both for staggered bloom time) and it works fine. I don't think there is a wrong way to sow poppies- they are so carefree!

By the way, what kind of poppies are the ones you are trying to grow? Hope you have good luck with them ;-)
CMK

CMKTammy

I normally scatter the seeds as soon as the ground warms up. So that's sometime in march or early april. Same goes with cosmos.