In LA your best window will be just a little later than right now. You want to avoid working your trees during the heat of the summer, with the exception of a few tasks that don't involve cypresses. Even though you won't get a frost, your hinoki will go mostly dormant from Dec-Feb. So your two windows to do work would be spring and fall (fall in this case might even be late October - depending how hot your September is this year).
Yes the foliage gets tighter - to a point. Hinoki cypresses are extremely difficult, if not impossible, to get to bud back on old bark. Constantly work to thin your outer foliage pads to allow light and air to get into the middle of your tree. Otherwise the tree may start to drop its inner foliage, and once it's gone, it may be gone for good. Likewise be careful about removing small bits of inner growth until you are certain you won't need them - ever. If you aren't careful, it is very easy to end up with a hinoki cypress that looks like a poodle, with tufts of foliage at the ends of bare branches. Once the growth gets away from you, it is very difficult to get it back.
