It's DXB - all the outlets are open 24 hours so you can pretty much get whatever you want, food-wise at any time! But if you mean in the lounge, then yes, you can order anything off the menu at any time. It might take a little bit longer when ordering "out of hours" but you have time...

As for sleep, depends how much of a light sleeper you are - I think for getting some proper rest, it sucks. You could probably have a nap but I don't think the "quiet rooms" are all that relaxing or even quiet. Sleep as much as you can on the plane I think, then kill time in the lounge with a one hour spa appointment and breakfast etc. Your 6.5 hour transit will end up being about 5 hours taking into account security and boarding time. If you do nap in the lounge, I would bring some ear plugs from the flight and the eye shades.