You may be able to get extensions on your B-2 visa, but if that expires and you have still not received I-526 approval, it may be best to make arrangements to leave the U.S., wait for I-526 approval, and go through the U.S. Consulate for your conditional permanent residency. Overstaying after expiration of the B-2 can be problematic.
The complete adjudication of your I-526 petition is unpredictable. Based on your question, it is more likely than not that the processing time will exceed your May 12, 2014 date. You have the option of attempting to extend your B2 visa, but a conflict of intents may make a positive outcome difficult. It is important to mention that overstaying on a visa may bring unnecessary problems.
An experienced EB-5Attorney will be able to assist you. First, the reality is that there is no predictability of how long it will take to obtain an approval on the I-526 petition. Secondly, the length of your B-2 visa does not limit your stay in the U.S. In fact, you may arrive in the U.S. a week before your B-2 visitor visa expires and the U.S. Customs and Border Protection inspectors at the air-port may authorize your stay in the U.S. beyond the expiration of the B-2 visa.