client wants me to watch their dog from 7am-8:30pm, I feel like Im not paid enough to watch and stay home all day for a 13+ hour day. How do i tell them i can only watch until a certain time?

I have to assume this request is for daycare. As a daycare provider, you establish the hours of operation. Let's say, drop-offs begin at 7.30 and pickups must take place by 5.30 or 6 pm. Anything later should incur an extra charge, a late fee, if you will. Take a look at what doggie daycare facilities charge in your area and their rules.

Put the doggie daycare hours in your profile so customers know.

Your other option is to not consider this clients booking if you cannot provide the time requested, possibly another sitter would be willing to do it.