Here is a common question from a seller to the Showing Service........."Can I change that appt to .............?  Now is not a good time for me."    Let me set the stage on this situation for you. 
Home is listed and Centralized Showing calls to let you know a realtor wants to show your home..............your feeding your daughter and its inconvenient so you ask if another time could work,  example:  "Can you ask the realtor if they can make it from 2 - 3:00 instead of 12:30 to 1:30?"   CSS rep says, I will find out and get back with you.   You go on feeding your child and are confident that this will be worked out.   Chances are it will not work out.   Making another phone call for CSS takes time and the realtor may not pick up so a message is left.  Keep in mind that the realtor who is setting the appts is trying to fit 8 showings into the time frame of her buyers' schedule---it is hard to do if everything works out perfectly but if someone needs a call back and change in the order, many times that showing will be passed by the realtor.  As a seller, keep this in mind---------making your home 100% accessible will insure you get every showing, and each showing is SO important since that could be your buyer!