Keep in mind when planting that Copper Rose is thought of as hardy, so it can be safe to leave outdoors for the majority of winter (although if in doubt, using a row cover is often a good idea).
By our calculations, you should look at sowing Copper Rose about 49 days before your last frost date.
Ensure that temperatures are mild and all chance of frost has passed before planting out, as Copper Rose is a hardy plant.