Mary Mosswas the mother of William Booth and the second wife of Samuel Booth... (wikipedia)
Set the kitchen timer for 10 minutes and tell them it is your time (to work out).
Set a time and keep it as if it were a really important appointment. You will fail if you say you will work out when you have time. There will always be something else to do. Five a.m., 9 p.m., at lunch, during commercials whenever you get a chance.
If you really want to do something, you'll find a way. If you don't, you will find an excuse. I don't know who said it, but I live by that motto.