I'm no doctor, but I did read 3-6 weeks for children and 6 to 16 weeks for adults (see below). The interesting part says that the more you move it, the slower it heals. So his working out and throwing now to get ready for Miami can actually make the healing go slower.
My GF and I were T-boned on July 3rd by an SUV making an illegal U-turn from the side of the road on my Heritage Classic. She broke 9 bones/ribs, etc. Including her tibia and clavicle. Her leg is at about 90% now, ribs are better but her clavicle still hasn't fully healed. I bust her chops all of the time saying Tony will be back before you! She says no way will he be back and healed by November 22nd. I guess the point is, if we are 2-7 then, why should he risk it. If he really wants to play this year he could still wait a few weeks. His call I guess.
The time for a broken collarbone to fully heal depends on the severity of the injury. In children, complete healing may take as little as three to six weeks. In adults, six to 16 weeks or more are often necessary for a collarbone to heal solidly.
Unfortunately, during that time there is no way to completely immobilize a collarbone fracture to keep it from moving and, thus, speed healing, as can be done using a cast on other broken bones, such as a wrist, arm or leg. Because of the broken collarbone's location in your body, a cast is not an option. However, a shoulder sling can help keep a collarbone fracture in place, reduce pain and allow for healing. The broken bone will move a bit whenever you move your shoulder, and that can often be painful during the healing process. A significant amount of shoulder movement may slow healing.
