I'm no expert on how long it takes green deer antler thoroughly dry, but I have also always waited a year before using any for knife handles, buttons, and handles of various sorts. I've been told that it may take less time if you cut up an antler into smaller pieces before you set them aside to naturally dry/cure. This allows the air to get inside the pithy portions of the antler and dry out better and faster.
I've found after cutting, the hard tine tips can usually be cut into buttons or used for handles or powder measures after about 6 months. The portions closer to the crown base may still need a year to dry out the interior even after you cut them. If you test drill into the pith sooner and find the interior is not dry, you could set the piece aside for a few more months to dry.
Years ago I was warned against trying to speed up the drying process by placing them in direct sunlight or at low temperature in a stove. I've seen some antler develop cracks due to the stresses involved when you try to artificially dry them out too fast.
Gus