I've found that it's better to leave the pod on the plant - But you have to make sure that it's upright. If it's leaning or hanging down, the seeds will fall right out. I have propped mine up with a twig to avoid that (learned the hard way!). The pods ripen very quickly, so it's sometimes hard to catch them before they tip over.
You'll know they're ready when the top looks like a salt shaker (it opens up underneath the crown looking thing).

I hope that helped a bit?
Melissa

The poppies have flowered and lost their petals
At what point can I remove them from the bed and still have viable seeds???

I leaves the pods on the plants also. The pods will turn brown and you will notice the tops of the pods start to have little openings for the seeds. That is when I pour the seeds into a container by tipping the pods. I am also sure it would be find to harvest them at that point since the seeds are mature.

I put up a link to Mr. Brown Thumb, who has a nice photo of the color change and the seed pod opening.

Here is a link that might be useful: Poppy Seed Pod Opening and Color Change

I take the toe of a stocking and wrap it over the pod, securing it with a rubber band. When the pod flops over, the seeds will fall into the stocking when they are ready. Then you can just cut off the pod when you collect them. You won't lose many seeds this way. Happy gardening!

I cut the pods off about 10 inches below the stem and hang them in small bunches upside down. After they dry I put a small hole in the bottom of the pod to get the seeds out. I then keep the entire dried pod with stems and use them for dried floral arrangements. I have alos found additional poppy pod and seed information at the following link.

Here is a link that might be useful: Poppy pod and seed information