I have had trouble taking a day off away from three days off as well and moving it when there has been adequate coverage. The only time that you will see one day off is with the FX day. It allows them to cover a 7 in 7 with a month to month transition. One way to then move it is to get a trip with a 24+ hr sit with at least three days to the day off, then you can move it. I have done that plenty of times.