I read you're supposed to cut oriental poppies the evening before they would open, when just a little color is showing. Then sear the stems and place them in a deep container of warm water. They should then open the next day and last about 3 days. I have only used them when the customer told me they only needed the flowers to look good for a single day event like a wedding or party. If you sell them to people at a market, you should warn them that they won't last long or they may feel you are selling them old flowers.

There was another thread on poppies recently. I don't know how to post the link, so just search for "Oriental Poppy" and you'll find it.
Kirk