It's strongly implied that the museum is open on Holidays, but to be on the safe side, try e-mailing to the Mexico City official tourist office (http://www.mexicocity.gob.mx/contacto.php?cat=50300&sub=0) or the museum itself (http://www.gobiernodigital.inah.gob.mx/mener/index.php?id=33).
Something is not right. This message is just to keep things from messing up down the road