How would you go about explaining this to customers?

I have had a thousand leaflets printed and am hoping to start a small dog walking business in my local area. I also work as a nurse however and do approximately two thirteen hour shifts a week. The way the shifts work out on the rota means that sometimes I will not be available for four days during the week, at other times I am available for five or six days on the trot. Would potential customers find this unnaceptable? Would they expect a dog walker to be available most days? How would I go about explaining this to them without putting them off? Any answers would be appreciated thank you.