No. There is no IRS rule that limits how high your time-space percentage can be. I have successfully defended providers in IRS audits who claimed a 98% time-space percentage when caring for children 24 hours a day, seven days a week. I have also successfully defended providers who did not care for children 24 hours a day, but had several rooms used exclusively for their business and had a time-space percentage over 65%.
Don’t hesitate to claim all the hours you work in your home, particularly when children are not present. Keep at least two months of daily records showing your work hours (cleaning, activity preparation, record keeping, etc.) when children are not present in your home.