My Cat Has Had Kittens On My Bed, When Can I Move Them?

You are loved and trusted! Mother cats won't deliver anywhere that they feel threatened. Usually they look for a cubby hole out of the elements, and somewhere that they are going to be safe from predators.
Your new mother is very trusting in you, and she feels every confidence that you aren't going to hurt them. Clear a spot in the closet, and let her know that it's there by showing it to her.
Repeat this if she doesn't seem too interested in it. She might then consider moving them there, especially if there is something in there that smells like you believe it or not.
The mother is going to respond to you, whom she loves and trusts, and SHE will take the kittens there if she sees fit. When she is comfortable with you touching them, she will let you touch them and even coddle them.
That is when you show her that you are taking the kitten to the new safe area, and she might accept that, or she might not. If not, then try another area of your room, but keep them in a large box if you can. Hope this helps, good luck surrogate mom.

You could move them now but if your not to bothered I would also give them the bed cover because it will have a scent thats familiar to the on it

The cat will just keep moving them back. They are stubborn little so 'n' so's.  My cat moved her litter to our airing cupboard behind the hot water tank. The pipes running to the tank get boiling hot at night and I was worried so I made a safe hidey hole for her under our stairs. She just kept moving them back there. We just got to trust their instincts (but I can understand how it could be a tad inconvenient to accomodate a litter of kittens in the middle of your bed...hehehe...good luck.  I hope you have more joy trying to find an alternative place that we did  :-)

My cat is under the bed for 50 hrs. No food or water. What should I do?

I believe you should let them lay on your bed until about 48 hrs.