It would be normal for the pressure to change on a cold night. It is just the air molecules trying to huddle together to keep warm. The further loss is a little troubling but the gas is going to be at 6oz. pressure and that makes a lot of difference. If you are concerned about leaks, mix a spray bottle of Dawn and water 50/50 and spray the joints while watching for foamy bubles. Keep your eye on the joints you have already tested; sometimes it takes a while to make the bubles.
Like he said, "if it holds for 2 hours, its good to go".