In a short arm cast that covers three of my fingers for a server bone bruise othro hasn't given answer for how long to expect to wear it thoughts ??

Weeks not Months: A "bone bruise" is actually a collection of blood under the periosteum (fibrous "wrapping" of the bone) and since the circulation is not great it take a longer time to resorb the blood than an ordinary bruise. The fact that a cast was applied suggests that there also may be a tiny fracture (called "avulsion fracture") along with the bruise. 6-8 weeks is the usual number given for complete healing