The answer to this question would not be 100% as you don't spend 100% of your time in your "office" working. By working, that would entail the hours in which you're caring for children. And if children are not present, then you may consider the time of activities that are business related, such as updating meal menus, answering emails, running invoices, etc.
As such, calculate the denominator which is the total amount of time AVAILABLE for you to work which would normally be the entire year (24 hrs/day x 365 days) or if you started the daycare after Jan 1, 2017 then you would base it on that number of days.
As for the numerator, it would be the accumulate number of hours per year that you spend caring for children and performing business related tasks when children aren't present.
Example:
My wife cared for children + performed administrative tasks for 3134 hours of the year and started the business on Jan 23, 2017 so there was only 8208 hours available for work in the tax year. Her time % is 38.18%.
