See whether you can book a free timed entrance ticket. If you can, the are open. If you can't, they are either closed or booked solid. You really need a (free) timed entrance ticket. You may not be able to get in -- or may face a very long wait -- without one. Remember to print out your ticket. A great museum and well worth the price :)
Trust the voicemail. The suggestion above is also good for other days - if you can't get tickets for that day then they are closed
Pray that they are open!!!
Thanks! Your answer is awaiting moderation.