I think you should practice any and everytime you have the opportunity, no matter whether you have a stand to shoot from or not.
I shoot in my basement a couple of times a week. There I can barely squeek out 20 yards (and have busted arrows on concrete:0)). Closer to season I do as much treestand practice as possible. For the most part I shoot about the same from a tree as from the ground.
Jim
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