If you intend to maintain your LPR status, you should not stay outside the US for more than 6 months. So assuming that you and your husband leave the US in August 2011 and you return to the US in December 2011, you will need to obtain his signature on the I-751 petition before you come back to the US. You will then need to file the I-751 before February 2012, along with supporting paperwork. I highly recommend that you hire an attorney to assist you with this process, to avoid unnecessary complications, and to keep up with your case if you are outside the US for a period of time. Please call my office if I can be of assistance.
Yes, you do have to begin the filinng process by November 2011 for Feb, 2012. There are two questions here. I- Can you file from outside the USA ?and 2- Can you accompany your spouse abroad with a conditional residency.? First- You can file to remove the conditions from outside the USA, however you may have to be available to answer any questions USCIS has in person. Second- You can accompany him, however it is best that you have an attorney go over your paperwork and dates of departure and re-entrance into the USA to make sure you will be able to re-enter