Ann,
Based on your HLA type, they can easily look up whether or not there are matching volunteers in the bone marrow donor registry, so I expect you will know within a week or two after the doctor requests the search. They took only a couple of days to find two potential matched donors for my wife in the U.S. registry. They also search other registries around the world. If you know your HLA type, you can even
search the U.S. registry yourself.
However, those are
potential donors, and it can take months for the entire process of contacting, scheduling, and testing potential donors to see which of them are available, willing, medically qualified, and a confirmed match. The National Marrow Donor Program says this can take 2 months or more. Doctors routinely tell patients to expect the process to take 3 to 6 months because it sometimes takes that long. Finding matching cord blood units (rather than bone marrow or stem cell donors) is typically faster. In any case, the sooner they start the search, the better.
You can read more about this on the NMDP's
The Search Process page.