Certified GKH Gardening Expert
First be sure that Cedar of Lebanon is suitable for your geographical area. It's a Mediterranean tree and cannot take the extreme cold of USDA Plant Hardiness Zone 5. If you are in Zone 6 it will be borderline, but check with local nurseries and arborists and look for other trees of this species in your area that are growing well.
And you must provide plenty of space for this large growing tree.
Spring is the best time to plant, when the trees have a long growing season ahead to get established. But of course you need to have resources and time to irrigate.