I have two master’s degrees. I didn't apply for OPT using my first master's degree, I used my second master’s degree to get my OPT (at that time, I already graduated from my 1st master’s degree for one semester; I studied those two master’s degrees at same time.) My understanding is you can only get one OPT for one level degree(s), for example, one OPT for master's degree no matter how many master's degrees you get, one OPT for Dr. degree, no matter how many Dr. degrees you have. If you don't apply for OPT using your 1st mater's degree, you still have chance to apply for OPT using your second master's degree. But you have to apply for OPT before you actually graduate from your master's degree. In past, you can apply for OPT within 6 months after your graduation. The best way is to confirm with your International Students Office. Good luck to you!!