Doreen is generally regarded as a hardy plant, 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).
Growing Doreen from seed
By our calculations, you should look at sowing Doreen about 90 days before your last frost date.
Transplanting Doreen
Doreen is hardy, so ensure you wait until all danger of frost has passed in your area before considering planting outside.