I changed my hours as my clients changed and I now work 8am to 4:45 but my official hours are 7:30 to 5pm because those are the limits that I'm willing to work within. If you have to make the change in hours to be happy and healthy and take care of your own family then you have to do it. You will learn to accept only the clients who fall within your limits and not to let anybody push you into working hours that make your life miserable.

Do any of your current parents have hours outside 7:30-5? If not then go ahead and make the change with a few week's notice. If you are going to lose clients due to the change then give them a month's notice minimum. I hope it works out well so you are happier. I'm not a morning person at all so I know my limits!