I would state:
What distinguishes my time from company time is anytime I am not scheduled to work or am not being paid for my time is my personal time (although if needed my time can become company time at anytime). Company time is when I am scheduled to work and am on company time. When it is company time, it is time to be at work in a timely fashion and be doing my duties to the best of my ability.
That would show you understand the difference but at the same time you are showing that you have full availability and even if it your time if you are needed and they contact you, you will be reliable. At the same time when you talk about company time make sure to show how well you will use the time that they are paying you.
I hope this will be of help to you.