Check with your school's

international student advisor.

My understanding is if you didnot take OPT when you applied for graduation for the first Master, you lose the chance for the OPT for Master. There is no OPT for the second Master. You may get a Master but didnot apply for graduation, and continue for the second master, then you still can apply for OPT for Master.

But please check with your school's advior on this one.