I usually put them on the north side of my house so that they only get some weak UV in the morning and late afternoon. After a week I put them under my willow tree and let the filtered midday light hit them. After a week there I put them out in the full sun. I may get a few minorly burnt leaves, but they make it through or just fall off.
My trees under the grow light this winter got a little leggy so I pruned back some of the new branch growth anyway. So the majority of my leaves are already UV tolerant.
Is your tree from seed or is it an actual grafted Haas plant?