What are suitable seasons for transplanting evergreen hedge shrubs? Is winter okay?
The best time to transplant is the spring or early fall since temperatures are cool but not too cold. Whenever a plant/shrub is transplanted some of the plant/shrubs roots will be cut and the remaining roots will need to resettle to be able to draw nutrients and water out of the soil to survive. For this reason it is important to pack down the soil around a newly planted shrub and to water generously for the rest of the summer. I have attached a link from the University of Illinois with a bit more detail included in it. Even though this link addresses a fall transplant the info will also work for a spring planting.
The winter would not be a good time for transplanting. The plant has gone into dormancy at this point to protect itself from the freezing cold temperatures. The ground is also helping to protect the roots from the cold as well as helping to keep the roots from drying out in the cold air. If the plant is dug up the roots will be exposed to the colder, drying air and they may snap off as well since they are intertwined with the frozen earth and are not flexible when frozen. The soil will not be able to mold itself around the roots and the roots will most likely freeze and die killing the whole shrub.
Lucky for you , you can take the winter off and save the hard work for the spring! Happy transplanting in the spring.