In order to answer this question correctly we need to know where you are in the system. Perhaps the alien that you posted bond for was granted relief by the immigration court. Alternatively, perhaps the person was picked up by ICE for a violation of the bond conditions. In either case, the first step is processing by ICE of the alien and cancellation of the immigration bond. This step can often times take ICE a while to complete.
After cancellation of the immigration bond, the Debt Management Center will send a notice to the person who posted the bond that the bond has been canceled. Once you have this notice, you can complete the paperwork necessary to file for receiving the money back from the federal government. You can get more details on this step here. The last part of the wait is waiting for the debt management Center to issue you a check.
With these steps in mind, if ICE has already notified the Debt Management Center, the debt management Center has sent you the notice of cancellation, and you have filed to receive the bond back, you should typically receive a refund within six months.