Hmm, interesting question.. My "guess" would be that you can take them together. Multivitamins have calcium, magnesium, and vitamin D all together. So logically, you can take them at the same time.
I take my calcium, B 12, and Vit D all together. Some of my calcium also contains magnesium. I think you are fine doing them all together.
i'm going to continue to take them together.
there aren't enough hours in the day to space out all of my supplements & my synthroid.