Changing the fixtures only takes a day or two in labor as long as after removing them there are no items that need to be addressed, such as; the sink and vanity which when removed may disclose water damage or most often shut off valves that need to be shut off, if in removing them there are no items that need to be addressed, such as; the sink and vanity, once removed may disclose water damage or most shut off the valves. I feel it's extremely important to have a shut off that allows us to stop water flow to that specific fixture to change out the sink without shutting down that main water valve, or if the shut off fails to shut off the sink, the valve can be shut off easily till it is fixed. Also there is often rot from a previous leak that might have to be addressed before any new installation takes place. Another problem is if the walls are out of square.