Poppy seeds require a period of cold to germinate and grow, so they generally do best when planted in the late fall or early spring. Ultimately, where live will determine the best planting time for your poppies. Here are some general guidelines: 

• If you live in Zone 6 or warmer,  you might have the best luck preparing your growing area in the fall and sprinkling the seeds (poppies prefer to be direct seeded into the garden). They will germinate in the early spring.
• If you live in Zone 5 or colder, sow the seeds in the soil as soon as you can work it in the spring. Poppies are very cold tolerant, and can handle frost and even some snow, so don't stress about the temps dropping again.