Why is this going to be 36 hours? I am an old lady, have 2 grow spaces set up and I could get 6 plants to "someplace safe", tear down my grow spaces, and have everything looking normal in a matter of hours. The landlord visits and the reverse would only take a couple of hours. As a side note, I am curiolus why you are going to put your plants in a dark period before going to flowering anyway? This seems like it would cause excessive stretch with no real benefit?
If you put the plants in bags, you will have to keep the tops open--they do have to breath and they do transpire. I wouldn't recommend the attic unless you are having exceptionally cool weather. When it is 80 outdoors, the attic can and generally is over 100 degrees. However, I see no reason that you should not be able to pull this off with no hitches. As multi said, the plants might be a bit disheveled (another reason not to rush to flowering), but they should be fine. They really are quite resilient while in veg.